There are many reasons for the for the boiler loosing pressure, so what can it be?
If your boiler has been working fine for many years then all of a sudden it starts to go to lock out because the pressure has dropped, most people think they have a leak. They call in the local plumber but,he cannot find any form of leak anywhere and he says you must have a leak under the floor somewhere, but the problem still exists so what can it be?
First you have to think, have you noticed any change in the boiler sound when running, or anything different but thought oh, that's ok. Has it been making any strange noises, has the pressure gauge been going up and down when running. Do you have to top the pressure up regular. If so how long has this been going on.
Next, when was the boiler last serviced, was it a 5 minute service like British Gas do or was it a strip down, when I say the 5 minute service this normally involves taking a combustion reading, and if the readings are ok, then it's signed off for another year as serviced.
Most of today's modern boilers are pressurised and have an expansion vessel fitted either internally or externally. The vessel needs to be checked each year, as over time it will loose its pressure. Once the vessels pressure has gone the boiler has nowhere for its expansion to go.
The pressure on the boilers gauge will start to rise as the boiler heats up. Because the vessel is no longer working the excess pressure is released through the pressure relief valve slowly, you may not even notice it happening. When the boiler is off and starts to cool down, the pressure will start to drop, sometimes down to zero.
If the boiler loosing pressure has not been serviced correctly, according to the boiler makers instructions then problems do happen. One of the major parts of the service is the expansion vessel. It needs to be checked without fail, otherwise, eventually the boiler will start to have problems and stop.
Most of the time when a call comes in for boiler loosing pressure we are told by the customer that they think they may have a leak somewhere, or they have been told by another plumber that they have a leak under the floor. This is for around 90% of the calls we take.
The other call we get is that the pressure relief valve on the boiler needs to be replaced because it's leaking, or the valve has been replaced and the boiler is still loosing pressure. So what is the problem?
The answer has already been mentioned above. It's the expansion vessel.
Most of the calls we attend re boiler loosing pressure are due to the expansion vessel. What has happened is the vessel has lost its charge so is now not working, and the expansion has nowhere to go other than out of the discharge valve.
Most of the time the vessel can be saved and be recharged, but if the vessel is full of water it may have already started to rust and corode inside and may not recharge properly, if this is the case then you will need to replace it.
With a correctly set vessel the boiler runs a lot smoother as does the pump. When the vessel has lost charge it is putting pressure on the pump and you will find the heating takes a little longer to heat up.
Most people don't realise that the expansion vessel plays a big part in the boiler working efficiently, it make it run smoothly.
So if you have a boiler loosing pressure, ask your engineer to make sure the expansion vessel is set at the right pressure a. According to the boiler makers instructions.