Pressure vessel problems?

Is your boiler losing pressure through its PRV (Pressure Relief Valve)?

Are you constantly topping up the boiler pressure to find it’s dropped back down?

When the heating is on the pressure gauge is rising over 3.0bar of pressure?

These are all symptoms of a faulty pressure vessel (also known as an expansion vessel). Pressure vessels can be built into the boiler or installed onto the heating system pipework. An expansion vessel works by having a pocket of pressurized air inside a vessel separated by a rubber membrane.

There are a couple of ways a pressure vessel stops working:

Over time the chamber of air inside the pressure vessel will dissipate, this is from the air slowly passing through the membrane (similar to a party balloon that was full and a few days later has shrunk).

The rubber membrane has broken and there is no longer air to compress against

The pipework to the expansion vessel is blocked

How do we fix these issues?

We drain the pressure from the heating system and recharge the pressure vessel back to 1.0bar.

If the membrane has broken, the pressure vessel cannot be fixed. It’ll need replacing.

Check the condition of the water. If the water is black with evidence of sludge and debris it is likely to be blocked and the pipework will need replacing or flushed/cleaned out.

Temporary fix

A temporary fix would be to drain a single radiator from the system. By leaving this radiator full of air it would act as a pressure vessel allowing the heating system to compress the air inside the radiator. This is only a temporary solution as this would mean no heat would come from the radiator.

We recently did this for a customer based in Great Haywood just outside Rugeley. We ordered the new pressure vessel for inside his boiler, while we waited for the pressure vessel to arrive we emptied the small radiator in their downstairs cloakroom. This allowed them to use the heating without issues until we could get back and replace the pressure vessel.

If you suspect your pressure/expansion vessel isn’t working correctly, then get in touch with us at DPJ Plumbing, Heating and Gas. We are able to diagnose what is at fault and how best to fix this issue.