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20 years' troubleshooting experience
Deep diagnostic knowledge to help resolve complex alarm codes and system faults.
Remote support where possible
Phone and video support designed to guide you through basic pre-visit checks and resets.
A practical guide before you book a repair
Heat pump troubleshooting often starts with a few sensible checks, and that's exactly what we help you do in Reading. We know a fault code can look dramatic when the cause is something as simple as a blocked filter, a closed valve or a setting that's been knocked. Berkshire Hampshire Heatpumps Ltd has put this guide together to help you spot common issues with air source and ground source systems, along with MVHR units, heat recovery systems and pool heat pumps.
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That matters because catching a small problem early can save you time, avoid an unnecessary call-out and help you explain the fault more clearly if you do need us. You might find your outdoor unit has restricted airflow, your glycol level has dropped, or your system just needs a safe reset after a power cut. If the fault stays put after the basics, we can step in with experienced support from Berkshire Hampshire Heatpumps Ltd.
Please note: This guide is intended for basic troubleshooting only. If you're unsure or your system continues to display faults, contact our experienced engineers for professional advice.
Ground source heat pumps troubleshooting
HP / LP Alarm: Commonly referring to an issue with flow; high pressure / low pressure
HP Alarms, in general, indicate a flow issue leaving the heat pump to either the hot water or the heating system. In other words; a restriction of some sort, preventing the intended flow / return, to and from the heat pump.
LP Alarms frequently indicate a flow issue coming into the heat pump from the ground array (outside pipes in the ground). This may signify that either a faulty pump or faulty valve is to blame. Other possible common diagnoses could suggest a restricted filter or glycol (antifreeze fluid) issue.
The initial areas for investigation would be to check whether there is:
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blocked filter
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faulty pump
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faulty valve
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glycol leak
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refrigerant circuit issue
It’s also important to note that there are two main types of ground source systems:
(1) a pressurised – this can be identified as having an expansion cylinder and a pressure gauge to indicate the pressure of the ground array, which generally sits between 1-2 bar.
(2) non-pressurised installation – which will normally have an expansion reservoir (clear container) with glycol inside that should be around halfway full.
Suspected Glycol (antifreeze) Leak: – the fluid running around the system and ground array may become too low for operation.
If either the pressure gauge is reading zero [pressurised system], or there is little or no fluid in the reservoir [non pressurised] this can indicate fluid loss in the system which needs to be investigated by a qualified engineer. Prolonged lack of glycol in the system can be detrimental to the longevity of the system.
You may be able to identify fluid deposits within the plant room or on a heat pump connection fitting; however, there is a possibility of loss of glycol via pipe connections in the ground array.
Note: A small amount of glycol needing to be added infrequently is quite acceptable due to pressure and temperature fluctuations that occur as part of the system operations.
However, constant pressure loss and the need to add a larger volume of glycol may indicate a more fundamental issue with the integrity of the ground array and will require attention.
Air source heat pumps troubleshooting
HP / LP alarm: Commonly referring to an issue with flow; high pressure / low pressure
HP alarms, in general, indicate a flow issue leaving the heat pump to either the hot water or the heating system. In other words, a restriction of some sort, preventing the intended flow / return to and from the heat pump.
LP alarms frequently indicate a flow issue coming into the heat pump. If the fan is still operating as usual, it’s highly likely that there is an issue with the refrigeration circuit. However, a faulty pump or faulty valve could not be ruled out.
The initial areas for investigation would be to check whether there is:
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blocked filter
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faulty pump
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faulty valve
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glycol leak
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refrigerant circuit issue
Only a suitably qualified F-GAS engineer can fully investigate refrigerant issues due to the safety requirements in handling gases.
In some instances, flow can be restricted due to systems requiring a power flush. Over time, debris can build up within radiators and connecting pipework, causing ‘blockages’ that affect flow. A chemical flush may aid in dislodging debris and improving this.
MP Alarm: Refers to an electrical issue whereby the internal protection system has tripped
MP alarms indicate the heat pump's electrical protection device has tripped to protect other vital components.
This can happen frequently when properties are located remotely, with an inconsistent electrical supply, or otherwise during an electrical storm. These alarms can normally be reset with remote assistance, but a visit to the site could be required. In the event the alarm cannot be reset or occurs frequently, it is likely that a component has failed, and further investigation would be required.
Each manufacturer will likely have a set of unique fault codes or references built in to the system that may provide specific information or the location of the error for investigation. For further information, please refer to the relevant link below:
Heat recovery units troubleshooting
The unit is not operating
There is a minimum air recovery temperature required for the system to operate. If the home is below 16 degrees, the unit cannot run and will remain in alarm. The surrounding temperature must be raised by alternative means before the system can begin running.
Has the isolator switch been accidentally turned off? Quite a common occurrence, as these units tend to be housed in cupboards that often double up as storage – switches can easily be knocked and turned off without knowing.
These units use a compressor. It may be possible that this has seized or is not running and therefore the system will be unable to operate. Qualified engineers can initially test this, and a refrigerant engineer may be required to provide resolution.
Is there any demand? If the system has met either your hot water or heating temperature, it does not need to operate further until further demand is needed. Check your settings to confirm this.
The unit is noisy/noisier than usual
Some units may automatically increase fan speed because of a blocked filter or blocked / closed vent. Different manufacturers have pre-programmed alarms that can notify you of when filters should ideally be tended to. As a guide however, these should be cleaned every three months and then replaced annually during routine inspections of the system.
With vents – most commonly the exhaust recovery vent can sometimes wind themselves shut – if this occurs then the system cannot recover any air to operate. These should be easily identifiable and rectified simply by opening.
We’ve compiled some more specific issues related to manufacturer unit models in the links below, from our experience and available user manuals.
MVHR [Mechanical ventilation] units
Low humming noise and the unit not seemingly operating
The easiest place to start investigation of any unusual noises would be to see whether you can identify any loose ducting. If this is the case, the fix may be simple in reconnecting or tightening fittings. Once actioned, if there is no change to sound or operation, then a further issue may exist.
Other humming or buzzing sounds may indicate the beginning of a component failure, such as a fan or PCB. Some systems will provide a warning traffic light system that gives you an indication of where investigation is needed; otherwise, it would be advisable to enlist the services of a specialist to review.
Some rooms in my property feel stuffy. Why?
If the fan speed is set too low or not correctly balanced, the system may not be extracting/supplying enough air to each room to successfully remove humidity from it.
Another area for consideration would be to check whether any external ducts/vents are blocked or, alternatively, whether any internal ductwork is damaged or squashed. If air cannot flow through the vents and ductwork successfully, again, the system cannot perform its primary function of supplying/extracting air.
I can see water dripping out of the internal vents/pipework
Commonly, we see that when ductwork hasn’t been sufficiently insulated, condensation can collect in ductwork and eventually pool and ‘leak’ from the nearest opening. Often this can be from a vent and needs to be reviewed by a specialist.
Similarly, a condensate drain can be installed or attached to the system, however if this has not been connected properly or is damaged – the moisture will not be contained and may find a place to ‘leak’ out from.
An indicator lamp is yellow – what does this mean?
Some systems may have a small external control panel that uses a traffic light system to indicate how the unit is operating. An example of how this may work is as follows:
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Red [solid] for an issue that requires immediate attention by a competent person
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Yellow [solid] for an active defrosting cycle or [flashing] a minor issue to review
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Green [solid] that all is operating as expected.
Always refer to user manuals, if available, as each manufacturer may differ in terms of indicator warnings – this may save you any unwarranted expense in the long run.
Many people often don’t realise that their ventilation system will have filters that should be cleaned / replaced frequently. It’s really important to maintain these in order to have fresh, clean air circulating around your property as intended.
Swimming pool units
The unit has power but is not heating the water
There would be two main areas an engineer would initially test: the main circulation pump and refrigerant levels. Pumps can seize at any time – these may feel very warm to the touch or make a buzzing sound. Without this functioning, flow around the system cannot be produced.
In terms of the refrigerant circuit, you can perform a visual check to see if there are any fluid deposits that could indicate a leak – or review if there are any noticeable cracks/splits on the housing of the heat exchanger where refrigerant fluid could escape from.
Alternatively, you may consider ensuring the evaporator/condenser coils are clean and free from debris – as this can reduce the quality of efficiency.
Some initial areas you can review would be to check if there is power to the unit and/or if anything has tripped. Can you see any debris inside stopping the fan from moving?
On assumption that power is going to the unit, we’d then start to investigate whether the internal motor has ceased or another component, such as a capacitor, is preventing the fan from operating.
The unit is freezing up and barely working
Poor airflow can be attributed to this, and thus units should have a good amount of clearance around them, free of vegetation. In addition, regular maintenance in cleaning coils will assist greatly in ensuring the system upholds good air flow. The tools required to safely do so can be inexpensive to purchase and simple to action.
A professional however, may also need to check refrigerant levels, expansion valves and water flow if issues persist, as these are some common areas for systems freezing up.
I think there is a leak on the system
Differentiating between condensation and a leak can be tricky if you don’t know what to look for. It’s entirely normal for a heat pump to produce a large amount of condensation when providing heating, and often separate drain pipework will be connected to take this away. However, not all units are installed this way, some with a soakaway [gravel] underneath the unit for condensate water to drip into.
If there is water somewhere else on pipework away from the unit or you are just uncertain in general, take a video of the affected area and contact a professional for further guidance.
The breaker keeps tripping
In the first instance, we would suggest contacting a professional to review whether, electrically, all is sound with the load and wiring. Turning off the system until a site visit can be attended to would be a safe option.
Some components do trip electrics when they are failing, such as the compressor; however, this may not mean the end of your system. Depending on the age of the system and available parts, a small investment in repairing may give you further longevity.
General heat pump issues
High electricity bills
Frequently turning thermostats up and down uses more electricity that you think. In conjunction to having a home that is insulated well, a heat pump is designed to maintain a consistent temperature, which in turn uses less power.
Some systems have an immersion heater installed as a backup for emergencies. These are designed to ‘kick in’ when external temperatures are too low and your heat pump needs assistance to get hot water or heating to the desired range. If you have programmed your temperature settings too low, you may be unknowingly activating the immersion into action. As this function does not use electricity as economically as a heat pump would when using its compressor, your consumption of energy used will be much higher. In similar instance, if temperature settings are too high – your heat pump will be working harder and for longer periods of time to constantly meet this demand, which inevitably will increase your energy consumption.
It’s important to take good care of your heat pump, as some of the components are quite delicate. Improper usage, such as a prolonged high demand, can impair the performance of parts, which affects their ability to work efficiently.
High water consumption/bills
We’d advise initially completing a visual check for signs of damp spots or pooling patches of water around your heat pump and fittings. Common parts, such as safety valves, can degrade quickly in hard water areas or through constant use on the system.
Condensate or other waste pipework may have joints that have eroded or weakened over time and be ‘leaking’. Underfloor heating may need to have a specialist engineer review if, through the manifold, we can detect no return flow. This suggests there could be a valve failure or potential leak somewhere in your system.
If you cannot visibly see any issues, we would advise checking and noting readings from your water meter. If this is indicating water flow but you are not using any water, we would suggest that this indicates a possible valve failure.
As water can be very damaging to its surrounding areas, if you suspect the above, we’d advise to get in contact with us to discuss further or arrange an inspection of your unit.
Be advised; your water supplier will charge you for every litre of water lost, and therefore, once you suspect an issue, you should act quickly to investigate, as bills can become excessive very quickly.
Radiators are not ‘hot’
It is important to initially understand that heat pumps are designed to constantly measure external and internal temperatures to establish how warm your home should be. If your home is well insulated, heat will be retained far longer, meaning there is less requirement for your heating equipment to be in use and potentially at lower temperatures when it is – to just ‘top up’ demand.
Secondly, sometimes how we ‘feel’ may not match the recorded ‘actual’ temperatures and thus is sometimes why radiators may only be lukewarm to the touch.
There is always a possibility that pipework could be partially blocked – as debris can build within, without regular inhibitor being added to the system. It may be that a power flush is required with the use of special chemicals to break down and clear unwanted sludge in order that the correct flow can be regained.