A commercial boiler can be mechanically sound, regularly serviced and apparently operating normally while still using more energy than necessary.

The problem is often not the boiler itself.

Heating plant can waste energy because it:

• Starts several hours before the building is occupied
• Continues running after occupants have left
• Heats unused areas
• Operates at unnecessarily high water temperatures
• Starts more boilers than the building actually needs
• Repeatedly starts and stops
• Heats one area while another system is trying to cool it
• Responds to inaccurate temperature sensors
• Runs pumps and heating circuits when there is little or no useful demand

Before considering replacement of otherwise serviceable commercial boilers, reviewing the heating controls can be one of the most practical places to start.

Modern commercial heating systems can use time schedules, optimum start and stop, weather compensation, boiler sequencing, zoning and Building Management System data to match heat production more closely to actual building demand.

The correct strategy depends on the building and plant, but these seven checks regularly identify opportunities for improvement.

1. Match Heating Schedules to Actual Building Occupancy

The first check is often the simplest.

Compare the programmed heating times with the times the building is actually occupied.

Commercial heating schedules can gradually become disconnected from real building use.

For example, an office may originally have operated from 8:00am to 6:00pm but now be occupied from 9:00am to 5:00pm.

The heating system may still be working to the original schedule.

Check:

• Normal opening hours
• Staff arrival times
• Weekend occupancy
• Cleaning periods
• Evening use
• Shift patterns
• Tenant operating hours
• Bank holidays
• School holidays
• Seasonal closures
• Special events

Look for Permanent Temporary Overrides

Temporary overrides are particularly worth checking.

Someone may have overridden the BMS during a cold spell, late meeting or weekend event and never returned the system to automatic operation.

A plant room left in hand, manual or permanent override can potentially continue operating regardless of the intended schedule.

Check whether:

• Boilers are in automatic control
• Pumps are in automatic control
• Heating zones follow their schedules
• Override periods have sensible time limits
• Holiday schedules are actually being used

The objective is straightforward:

Provide heating when the building requires it, rather than simply running the plant because that is how the controls were set several years ago.

2. Review Optimum Start and Optimum Stop

A fixed heating start time assumes every winter morning requires the same amount of warm-up.

Buildings do not work like that.

A commercial building may require a long warm-up period after a freezing weekend but considerably less heating on a mild autumn morning.

Optimum start control is designed to calculate when heating should begin so that the building reaches its required temperature around the start of occupancy.

Instead of always starting at, for example, 5:00am, the controller can take account of conditions and adjust the start time.

Factors can include:

• Outdoor temperature
• Indoor temperature
• Building thermal response
• Required occupancy temperature
• Previous warm-up performance

A well-configured system can therefore start earlier when necessary and later when conditions allow.

What Is Optimum Stop?

Optimum stop works towards the other end of the occupied period.

Rather than necessarily operating the heating plant at full normal conditions until the exact moment occupancy finishes, the controls may be able to reduce or stop heat input earlier while stored heat within the building maintains acceptable conditions.

This is particularly relevant in buildings with significant thermal mass.

Why Optimum Start Can Go Wrong

Simply enabling an optimisation function does not guarantee good operation.

Poor results can occur because:

• Outdoor sensors are inaccurate
• Indoor sensors are badly positioned
• The system has never been commissioned properly
• Building use has changed
• Heating emitters have been altered
• The building fabric has changed
• The control parameters are unsuitable
• Manual overrides interfere with the sequence

If the heating still starts at 3:00am every day despite mild outside conditions, the optimisation strategy deserves investigation.

3. Check the Weather-Compensation Curve

A commercial heating system generally does not require the same water temperature on a mild day as it does during the coldest winter conditions.

Weather compensation adjusts the heating-water temperature according to outdoor conditions.

As the outside temperature rises, the required heating flow temperature can be reduced.

As conditions become colder, the controls increase the target temperature according to the selected heating curve.

For example, a system may require relatively high flow temperatures during severe winter weather but considerably lower temperatures when it is 10°C outside.

The exact figures depend on:

• Building heat loss
• Radiator or emitter sizing
• Heating-system design
• Required room temperatures
• Boiler type
• Hydraulic arrangement

Why This Matters for Condensing Boilers

Modern commercial condensing boilers achieve their best performance when the heating system allows them to operate under suitable condensing conditions.

Lower heating-water temperatures can help reduce return temperatures and increase the opportunity for the boiler to recover latent heat from its flue gases.

This does not mean simply turning every boiler temperature down as far as possible.

The building must still achieve its required room temperatures.

The objective is to use the lowest appropriate heating-water temperature for the current building demand.

Do Not Assume the Factory Heating Curve Is Correct

Weather-compensation settings should reflect the actual building.

A curve suitable for a poorly insulated Victorian building may be inappropriate for a modern well-insulated office.

The curve may need adjustment where:

• Rooms regularly overshoot their temperatures
• The building struggles during cold weather
• Flow temperatures remain unnecessarily high in mild weather
• Return temperatures remain consistently high
• Occupants continually adjust local controls

Changes should be recorded so their effect can be measured.

4. Check How Multiple Boilers Are Sequenced

Many commercial plant rooms contain multiple boilers operating together.

This provides:

• Modulation
• Capacity
• Resilience
• Better load matching
• Backup in the event of a fault

However, the benefits depend heavily on how the boilers are controlled.

A boiler sequence controller or BMS should determine how much plant is required and operate the boilers appropriately.

What Is Boiler Sequencing?

Boiler sequencing determines:

• Which boiler starts first
• When another boiler is enabled
• How firing rates are shared
• When boilers are removed from the sequence
• Which boiler becomes lead
• How operating hours are rotated

The objective is to match the available boiler capacity to the actual heating demand while maintaining reliable operation.

Cascade Versus Unison Control

There is not one sequencing method that is correct for every plant room.

With cascade control, the controller may attempt to meet demand using a smaller number of boiler modules before introducing additional modules.

With unison control, several modular boilers may operate together and modulate at relatively low firing rates.

Both approaches can have advantages.

The correct strategy depends on factors including:

• Boiler design
• Minimum modulation
• Number of modules
• Hydraulic configuration
• System load
• Manufacturer recommendations
• Required resilience

This is why commercial boiler sequencing should be properly commissioned rather than based on a generic rule.

Rotate Lead Boilers Where Appropriate

On suitable installations, lead/lag rotation can help distribute operating hours between boilers.

Without rotation, one boiler may accumulate substantially more operating hours and ignition cycles than the others.

A sensible control strategy can help balance usage while ensuring the plant retains sufficient standby capacity.

5. Prevent Dry Cycling and Short Cycling

Boiler cycling deserves particular attention because two related issues are often confused.

What Is Dry Cycling?

Dry cycling occurs when the heating plant repeatedly fires even though there has been no meaningful change in useful heat demand.

The boiler may heat the circuit, switch off and then start again without the building requiring additional useful heat.

Appropriate heating controls can include anti-dry-cycling functions intended to prevent this unnecessary operation.

What Is Short Cycling?

Short cycling describes a boiler starting and stopping repeatedly over relatively short periods instead of achieving stable operation.

Modern boilers are designed to modulate their output, but even a modulating boiler has a minimum firing rate.

If the building requires less heat than the plant can practically deliver, the boiler may quickly reach its temperature set point and shut down.

It then restarts when the temperature falls again.

What Causes Commercial Boilers to Short Cycle?

Possible causes include:

• Oversized boiler plant
• Minimum boiler output being higher than the current load
• Low system water volume
• Poor boiler sequencing
• Narrow control differentials
• Incorrect temperature sensors
• Poor sensor location
• Restricted water flow
• Closed control valves
• Incorrect pump operation
• Poor hydraulic separation
• Incorrect bypass arrangements
• BMS control problems
• Zone valves closing while boilers remain enabled

The controls and the mechanical heating system therefore need to be assessed together.

Changing a software setting will not correct an underlying hydraulic problem.

Likewise, replacing pumps or boilers will not fix poor control logic.

Why Cycling Matters

Excessive cycling can increase the number of:

• Burner starts
• Ignition sequences
• Valve operations
• Fan starts
• Pump operations

It can also indicate that the boilers and building demand are poorly matched.

When reviewing BMS trends, boiler starts and run hours can therefore provide useful diagnostic information.

6. Make the Heating Zones Match How the Building Is Actually Used

Most commercial buildings contain spaces with very different heating requirements.

A single control strategy for the entire building may therefore be inappropriate.

Consider an office building containing:

• Open-plan offices
• Meeting rooms
• Reception
• Corridors
• Toilets
• Server rooms
• Kitchens
• Stores
• Warehouses
• Training rooms

These areas are unlikely to require identical temperatures and operating hours.

Good Zoning Can Reduce Unnecessary Heating

A meeting room used for three hours a day does not necessarily need the same heating schedule as a permanently occupied office.

A warehouse may require a lower temperature than an office.

A kitchen may receive substantial internal heat from equipment.

Corridors and circulation spaces may have different requirements again.

The control zones should therefore reflect the way the building is actually occupied.

Check the Field Devices as Well as the BMS

A perfect BMS graphic does not prove the heating system is operating correctly.

If the BMS commands a zone valve closed but the actuator has failed open, the area can continue receiving heat.

Check that:

• Motorised valves operate
• Actuators move fully
• Pumps respond correctly
• Temperature sensors are accurate
• Sensors are positioned sensibly
• Local thermostats work
• Valve feedback matches actual position where available
• Control valves are not seized

Prevent Simultaneous Heating and Cooling

Buildings containing both heating and air conditioning require particular attention.

A poorly coordinated building can end up with:

radiators heating a room while the air conditioning is cooling it.

This wastes energy and can generate persistent comfort complaints because the systems effectively fight each other.

Suitable deadbands, set points and control interlocks should be used where practical to prevent simultaneous heating and cooling within the same zone.

7. Turn BMS Data Into Useful Information

A Building Management System can provide an enormous amount of data.

The value comes from using that information to understand how the heating system is actually operating.

Useful heating trends can include:

• Outdoor temperature
• Room temperatures
• Heating flow temperature
• Heating return temperature
• Boiler target temperature
• Boiler firing rate
• Boiler enable status
• Boiler stage
• Boiler run hours
• Boiler starts
• Pump status
• Pump speed
• Zone-valve position
• Control-valve position
• Heating demand
• Occupancy mode
• System pressure

Looking at several of these values together can reveal problems that would be difficult to identify during a short plant-room visit.

What Should You Look For?

Heating Outside Occupied Hours

If boilers, pumps or zones operate overnight despite the building being empty, investigate why.

Very Early Boiler Starts

Compare start times with:

• Outdoor temperature
• Indoor temperature
• Occupancy time

If the system starts at the same early time regardless of conditions, optimum-start operation may not be functioning effectively.

Boilers Firing Against Closed Valves

If the boiler is enabled while most zone valves are closed, review the demand logic and hydraulic arrangement.

Excessive Boiler Starts

Large numbers of starts with short run times can point towards cycling problems.

Zones That Never Reach Set Point

This could indicate:

• Insufficient heat
• Poor flow
• Sensor problems
• Valve faults
• Incorrect compensation settings
• Building-fabric problems

Simply increasing the boiler temperature should not be the automatic response.

High Return Temperatures

On a condensing boiler system, persistently high return temperatures may reduce the opportunity for condensing operation.

The cause could include:

• High flow-temperature settings
• Poor system balance
• Hydraulic arrangements
• Controls
• Oversized flow rates
• Bypass circuits

The complete system needs consideration.

Do Not Ignore the Heating Pumps

Commercial boiler efficiency is not only about boiler controls.

Heating pumps can also be unnecessarily enabled outside periods of useful demand.

Check:

• Pump schedules
• Variable-speed control
• Differential-pressure settings
• Pump run-on periods
• Standby pump sequencing
• Duty/standby rotation
• Whether pumps run when all relevant zones are closed

Pump control should be coordinated with the heating demand rather than treated as a separate system.

Check the Temperature Sensors

Controls can only make good decisions when the information being supplied to them is reliable.

A temperature sensor that reads incorrectly can cause the entire heating strategy to operate badly.

Common problems include:

• Outdoor sensor exposed to direct sunlight
• Indoor sensor positioned beside a heater
• Sensor installed in a draught
• Sensor affected by office equipment
• Failed sensors
• Sensors with calibration errors
• BMS points mapped incorrectly
• Sensors representing the wrong zone

An outdoor-temperature sensor reading 5°C when the actual temperature is 12°C can cause weather-compensated controls to request more heat than necessary.

Sensor readings should therefore be checked against reality rather than assumed to be correct because a value appears on the BMS.

Review Heating Set Points

Small changes to control strategy can sometimes avoid unnecessary heating without affecting comfort.

Review:

• Normal occupied set point
• Unoccupied setback
• Frost-protection settings
• Heating deadband
• Cooling set point
• Flow-temperature set point
• Weather-compensation curve

Avoid a situation where one control system is set to heat a room to 23°C while the air-conditioning system begins cooling at 22°C.

The heating and cooling strategies should work together.

Check That Frost Protection Still Works

Reducing operating hours must not compromise frost protection.

Commercial heating systems may contain pipework or equipment in:

• Roof spaces
• External plant rooms
• Loading areas
• Warehouses
• Service voids
• Other exposed locations

Frost-protection controls should therefore remain operational even when normal occupancy heating is disabled.

The objective is to stop unnecessary comfort heating without removing necessary plant or building protection.

Controls Cannot Fix Mechanical Faults

A controls review should not be treated as a substitute for mechanical maintenance.

The BMS may request the correct operation while the physical equipment fails to respond.

Typical examples include:

• Seized valves
• Failed actuators
• Failed pumps
• Blocked strainers
• Poor system balancing
• Failed temperature sensors
• Incorrect expansion pressure
• Air in the system
• Dirty heat exchangers
• Boiler faults

For example, rewriting the BMS sequence will not solve a heating zone that is cold because its motorised valve has mechanically failed shut.

The heating system should therefore be treated as one complete system incorporating:

boilers + pumps + valves + sensors + pipework + controls + BMS + building

Commission the Whole Heating Sequence Before Winter

A useful pre-winter controls review should test the complete sequence from initial demand through to heat arriving at the occupied space.

For example:

1. A heating zone falls below its required temperature.
2. The BMS registers a genuine demand.
3. The appropriate zone valve opens.
4. The heating pump is enabled.
5. Boiler demand is generated.
6. The sequence controller determines how much boiler capacity is required.
7. The boiler or boilers fire and modulate.
8. Flow temperature follows the appropriate control target.
9. The zone reaches temperature.
10. Demand is removed.
11. Boilers and pumps shut down or modulate according to the designed sequence.

Testing the whole sequence can reveal problems that are easily missed when each individual item of equipment is checked separately.

Record the Final Control Settings

Once changes have been made, record them.

Useful information includes:

• Occupancy schedules
• Holiday schedules
• Heating set points
• Flow temperatures
• Weather-compensation curve
• Boiler sequencing strategy
• Lead/lag arrangement
• Optimum-start settings
• Pump settings
• Override arrangements
• Frost settings

Without a record, settings can gradually be altered over time without anybody understanding what the commissioned strategy was intended to achieve.

Explain Overrides to the Site Team

Site staff should know:

• What can safely be overridden
• How long an override lasts
• How to return plant to automatic operation
• What should not be altered
• Who to contact when there is a problem

A good controls strategy can quickly become ineffective if every comfort complaint results in permanent manual overrides.

Review Performance Again During Cold Weather

A September or October controls review is useful, but some problems only become apparent when heating demand increases.

Consider reviewing performance again when colder weather arrives.

Look at:

• Occupant comfort
• Boiler run hours
• Boiler starts
• Gas consumption
• Heating flow temperatures
• Return temperatures
• Zone performance
• Optimum-start times
• Boiler staging
• Pump operation

This gives facilities teams an opportunity to fine-tune the controls using actual winter performance rather than relying entirely on theoretical settings.

Frequently Asked Questions

What Is Weather Compensation on a Commercial Boiler?

Weather compensation automatically adjusts the heating-water temperature according to outdoor conditions.

As outside temperature increases, the required heating-water temperature can normally be reduced.

As the weather becomes colder, the controller increases the required temperature according to the configured heating curve.

Does Weather Compensation Save Energy?

It can help reduce unnecessary heating-water temperatures during milder conditions and improve the overall control of the system.

On suitable condensing-boiler systems, lower water temperatures can also help create conditions that allow more effective condensing operation.

The actual benefit depends on the building and how well the controls are commissioned.

What Is Boiler Sequencing?

Boiler sequencing determines which boilers operate, when additional boilers are enabled and how available boiler capacity is matched to the building’s heat demand.

Different installations may use cascade, unison or other strategies depending on the boilers and system design.

Should the Lead Boiler Be Changed Regularly?

Many multiple-boiler control systems include rotation strategies that distribute operating hours between appliances.

Whether and how this should be done depends on the boiler plant and manufacturer’s recommended control strategy.

What Is Optimum Start?

Optimum start calculates when the heating system needs to start so that the building reaches its required temperature by the beginning of occupancy.

Unlike a simple fixed timer, it can take account of factors such as outdoor and indoor temperature.

What Is Optimum Stop?

Optimum stop can reduce or stop heat input before the end of an occupied period where the building can maintain acceptable conditions using its stored heat.

The effectiveness depends on the building and controls.

What Is Boiler Dry Cycling?

Dry cycling refers to boilers repeatedly switching on and off when there has been no useful change in heating demand.

Suitable control strategies can help prevent unnecessary dry cycling.

What Is Boiler Short Cycling?

Short cycling occurs when a boiler repeatedly runs for relatively short periods and shuts down before restarting again.

Possible causes include oversized plant, low load, poor flow, low water volume, unsuitable controls, sensor faults and hydraulic problems.

Why Does My Commercial Boiler Keep Turning On and Off?

There are several possible causes.

The boiler may be:

• Oversized for the current demand
• Reaching its temperature target too quickly
• Receiving incorrect demand signals
• Operating against closed valves
• Suffering from poor water circulation
• Affected by incorrect sensor readings

The plant should be investigated rather than assuming the boiler itself is faulty.

Can BMS Changes Reduce Heating Costs?

Potentially.

Correcting unnecessary operating hours, inappropriate temperatures, poor zoning or ineffective boiler sequencing can reduce avoidable operation.

However, the benefit depends on the existing system, and changes should ideally be verified using energy consumption and BMS trend data.

Should Commercial Boilers Run Overnight?

Only where there is a genuine operational requirement.

Normal occupancy heating may not be necessary throughout the night, although requirements such as frost protection, process heating, domestic hot water or continuously occupied areas may still need plant operation.

Why Are My Boilers Running When All the Heating Zones Are Closed?

This could indicate:

• Incorrect BMS logic
• A hidden heating demand
• A valve feedback issue
• Domestic-hot-water demand
• Frost protection
• Boiler control settings
• A hydraulic or control fault

The plant sequence should be investigated.

Commercial Boiler Controls and Plant-Room Reviews

Cherwell Heating provides commercial heating, boiler and plant-room support across Oxfordshire, Buckinghamshire and surrounding areas.

We work with:

• Offices
• Schools and colleges
• Hotels
• Healthcare buildings
• Industrial premises
• Warehouses
• Commercial landlords
• Managing agents
• Facilities-management companies

We can review:

• Commercial boiler operation
• Boiler sequencing
• Heating schedules
• Weather compensation
• Optimum-start operation
• Heating zones
• Pumps
• Motorised valves
• Temperature sensors
• BMS operation
• Short cycling
• Plant-room controls
• Expansion and pressurisation equipment
• Commercial boiler maintenance
• Heating-system faults

Our aim is to understand how the complete heating system operates, rather than simply changing individual control settings without considering the mechanical plant.

Before winter heating demand increases, contact Cherwell Heating to arrange a commercial heating and plant-room controls review.

Internal-link suggestions

• Commercial plant-room installation and maintenance
• Commercial heating servicing
• Commercial gas boilers

Sources checked

• UK Energy Technology List – HVAC building controls
• HSE – Gas safety for employers