Pressure issue on a combi boiler?

[Fab5Freddy]

The pressure on my fairy new combi boiler is low sometimes (in the red between 0-1) and I keep adding some water to the system via the inlet tap to bring it up to about 1.5 or so. However after a week or few days , it is back down in the red low pressure

I don't know much about central heating and boilers but does that suggest it is losing water from the system somewhere? I saw that when I let too much water in the other week and had the CH on high, the pressure went to about 2 or more it blew some water out of an external 'overflow' pipe, but nothing other than that.

It works fine, was serviced just before xmas and no issues - Is it an issue to worry about or should I just keep topping it up?

and for info, is the pressure only meant to be in the green range when it's in use? ie mine is on zero pressure when no hot water or CH is used.

Thanks

 

[ianmcd]

NO dont keep topping it up, you will rot the system constantly adding oxygenated water , get it sorted

 

[footprints]

May well be a faulty pressure vessel, by the sound of it. If lucky an engineer can repressurise the vessel if not might need replacement, but not uncommon to just need a pump up. This is not the repressurising you do with the cold water there is a tank inside the boiler which has a diaphragm with water on one side and a cushion of ait pressure on the other. Not a diy job though.

 

[Hugh Jaleak]

As above, you will need to get it looked at. Basically, water expands as it's heated, and to absorb this expansion a vessel is provided within the boiler to do this. If this vessel fails, the expansion has nowhere to be absorbed, and so operates the Pressure Relief Valve (PRV) and discharges excess pressure safely outside. You then come along, top the system back up again and the cycle repeats. Expansion vessel may be able to be recharged, of if it has failed internally, it will need replacing.

Under normal operation the pressure should be in the Green band at around 1-1.5 Bar when cold, rising, (but remaining in the Green band) when system is working.

 

[Deleted member 267285]

Check the pipe you are calling an overflow, if it’s wet at all it could be the pressure relief valve passing, the expansion vessel failed, or both. Have you any heating leaks?

 

[Fab5Freddy]

Check the pipe you are calling an overflow, if it’s wet at all it could be the pressure relief valve passing, the expansion vessel failed, or both. Have you any heating leaks?

Not wet, just blew some out the other week when I think I overfilled.
No leaks as far as I know anywhere.

 

[Fab5Freddy]

Thanks all. I appreciate the answers and will just call someone in.

 

[gas112]

go around all your raidator valves first and have a feel for dampness it could just be a small weep on one of them that needs nipped up