Why Is My Boiler Losing Pressure?


Is your boiler is losing pressure? Boiler pressure issues are one of the most common boiler faults and can cause boilers to not work for heating or hot water. Majority of the time the boiler is losing pressure due to a faulty boiler part or a leak somewhere in the heating system.  Whether your boiler is an oil boiler, gas or LPG boiler, system boiler or combi boiler, pressure problems are most commonly due to a leak either in the boiler or on the heating system.

The leak may not always be visible as pipework may run under floorboards. In circumstances like this you will require a further investigation from a heating engineer.


Causes of boilers losing pressure:

1) Faulty expansion vessel

A faulty expansion vessel in the boiler can result in boilers losing a considerable amount of pressure.

Expansion vessels or tank, their main purpose is to contain air and water from the central heating system in order to maintain the right level of pressure in the system. Expansion vessels can become defective over time and cause leaks through their valves. The diaphragm in the vessel can also become damaged overtime through wear and tear and pressure can get lost.

You may find you are having to top up your boiler a more than once a week. Sometimes the faulty expansion vessel can be repaired by re-pressurising it however if this doesn’t work it will need to be replaced.

Replacing an expansion vessel is a common boiler repair and can only be carried out by a qualified gas safe heating engineer. Get a free quote to diagnose your boiler pressure problem.



2) Faulty pressure relief valve


Also known as a safety release valve, a pressure relief valves on boilers help to prevent a build-up of pressure by releasing pressure when the level becomes too high. These valves can become defective overtime due to a blockage from dirt and debris in the heating system or the seal may have worn away.  Faulty pressure relief valves can then cause the boiler to lose pressure.

The best result is to replace the pressure relief valve, it may be that the expansion vessel is required to be replaced too. This replacement can only be carried out by a gas safe heating engineer.




3) Leaking radiators and radiator valves

Leaks on radiators and radiator valves are another reason for low boiler pressure. You may get lucky and find a visible leak on radiator valves or lock shields. In other circumstances this can be a difficult job to find as most heating system pipework is hidden under floors and walls.

Should a leak be present on your heating system you can try to add leak sealer or chase pipework to see any visible leaks. Its always best to instruct a qualified heating engineer to come and diagnose the problem first.




4) Leaking auto air vent

Auto Air vents are helps to remove air pockets which builds up in heating systems over time. These are usually located inside the boiler and can become faulty over time and therefore lose pressure through them through a consistent leak.

If you think your auto air vent is leaking instruct a gas safe engineer to come and inspect the boiler and the vent to make an accurate diagnosis.




5) Air in radiators

Air can build up in radiators over time, a main cause of this is if the heating system was recently drained and refilled.  When air has been bled from radiators this causes the pressure to drop in the system.

Whenever you release air from the system you must ensure that the pressure is topped up by releasing more water into the system. There is usually a valve under the boiler which will allow you to do this. You will need to keep an eye on the boiler’s pressure gauge and ensure that it dose not go past 1.5 mbar.

If you are unsure of how to do this, it would be best to get a gas safe heating engineer to come and inspect the boiler. 




6) Faulty pressure gauge

In rare circumstances you may have a faulty pressure gauge. This can cause the more serious problems as people will top up the boiler with more pressure than it needs. By doing this it can cause more problems with other parts in the boiler & system.

If you see that your boilers pressure is low, and the gauge does not increase as you let water into your system then you will know that there is a problem with your pressure gauge. These components on the boiler may be covered by the manufacturers warranty. If the warranty has passed you will need to get this replaced by a gas safe heating engineer.




7) Leaking boiler joints

Leaks are the leading cause of a boiler losing pressure.  Water in pipes expand when water is hot and over time soldered joints can become weaker causing leaks to appear. Leaks are commonly present on the filling loop.

If you find a leak on your boiler, contact a gas safe heating engineer to come and re-solder any lose joints or if necessary, replace any pipework that needs upgrading.

Once the work is carried out the pressure issue will need to be monitored to see if there is more pressure loss. It maybe that there is more than one issue causing this pressure drop.  Has your boiler lost pressure? Get your boiler and system checked over by one of our friendly local gas safe heating engineers.




Book An Engineer Visit

Want a professional diagnosis on your boiler pressure problem? Contact us now to arrange an engineer visit, we cover all of Torquay, Brixham, Paignton, Totnes and Newton Abbot. 

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