Boiler losing pressure every morning fixed in Wilmslow

A homeowner in Wilmslow got in touch because her boiler kept losing all its pressure. Every morning she found the gauge at zero, with no heating or hot water. She topped it back up to about 1 bar, as the instructions say, but the pressure slowly disappeared again. It had become a daily routine.

The boiler is a Worcester Greenstar 30Si Compact. When we checked it with the heating running, the pressure didn't rise a little, as it should. It climbed towards 3 bar, the point where the pressure relief valve opens to protect the system.

That pointed to the cause. A sealed heating system usually sits at around 1 to 1.5 bar when cold. As the water heats up it expands, and the expansion vessel takes up that extra water. Inside the vessel, a flexible diaphragm separates the heating water from a cushion of air. When the vessel can't do its job, the expanding water has nowhere to go and the pressure shoots up.

Here, the pressure relief valve was letting water out every time the system warmed up. When it cooled down again there wasn't enough water left, so the gauge dropped to zero. That's why the topping up never lasted.

We inspected the expansion vessel and found its internal diaphragm had failed. With a failed diaphragm, putting air back into the vessel isn't a proper fix, so the whole vessel needed replacing. The pressure relief valve also needed replacing after letting water out so many times.

We then:

• replaced the failed expansion vessel

• replaced the pressure relief valve

• brought the system back to the correct pressure

• carried out a full boiler service

• checked the heating and hot water were working properly

The boiler was back to normal, with working heating and hot water and no more pressure loss. The customer was relieved not to be refilling it every morning.

Not every pressure problem is the expansion vessel. Leaks from radiators, pipework or parts inside the boiler can cause it too, which is why we find the cause before replacing anything. Checking the expansion vessel is part of our boiler service, so a vessel that is losing its charge can be spotted before it leads to a breakdown.

If your boiler keeps needing topping up, find out more about our boiler repairs.