Boiler Pressure Dropping

[Julie1576]

Hi,
We have a Main Combi Eco that is losing pressure daily. The water is leaking from the pressure sensor valve or which we have changed the washer. This has not helped and the pressure is still dropping. We need to top up the boiler every day or so. Can anyone offer any suggestions please.

 

[TCCHeating]

If you have fixed the leak from the pressure sensor then you have a leak elsewhere. pressure the system up to 1-1.5 bar when cold, then turn the heating on. Check to see if there is any water coming out of the pressure relief valve (15mm copper pipe outside) as the system gets hot. Also check that the pressure gauge does not go too high on the boiler when hot ( the pressure relief valve will open when the boiler pressure guage gets to about 3.5 bar.

If all is ok with that, then you probably have a leak elsewhere on the system. Pipework under the floor maybe

 

[easyflow]

Look at the e/vessel or prv first.

 

[MANDATE]

I would suggest you set the water pressure with heating off and cooled down a little to 1.0 bar or 1.5 bar
Then turn heating on and watch the pressure gauge.
Water expands as it heats up. The extra volume is supposed to go into the expansion vessel (thats if there's room for it).
The pressure will rise and depending on what it rises to, will indicate if the vessel is at fault or not.
If the vessel has lost some of it's pre charge, then there won't be sufficient air space left . The water pressure should only rise approx 1.0 bar so it may go up to 2.5 bar which is OK.
But with insufficient air volume the pressure will go much higher and thats where the PRV does it's job by opening when 3.0 bar pressure is reached.
So first job, is to be satisfied the vessel is working as it should and pressure is not reaching the 3.0 bar that opens the PRV.
Unfortunately PRVs once opened often don't close again fully due to sediment on the valve seat, meaning it either needs to be cleaned or a easier option to replace with a new one.
Of course if expansion vessel and PRV are found to be OK, then the leak is elsewhere. Usual around radiator valve spindles.