Combi pressure drop every week

BenHarrison · 24 Jun 2010

Another quick question while I'm online, it's been annoying for ages now

The boiler pressure drops in about a week from 1.5 to about 0.2 and I have to top it ip to get the combi to fire up.

What could be the causes of this. I have checked for a ny leaks and all seems ok,also the pressure vale outisde is dry (was adised to check that).

Someone briefly mentioned Hyrdogen in the radiators could be the cause.... is this true if so how can I check for this?

What else could cause this please?

twgas · 24 Jun 2010

Try fixing a plastic bag over the end of the discharge pipe and see if it collects any water as the pressure drops - maybe during the night.

BenHarrison · 24 Jun 2010

Thanks, I will do just that.

If it does, is it hard to replace ??

Axel · 24 Jun 2010

It might be that the expansion vessel in the boiler has lost its air charge, so that when the boiler heats up it raises the pressure momentarily to 3 bar and then the PRV discharges, causing a pressure loss. Water would only show at the PRV outlet pipe when the boiler is hot, not all the time.

Either that or you've got a leak in your pipework or rads.

BenHarrison · 24 Jun 2010

How can I check the expansion vessel? I know what it is. Do I need a gauge? Thanks.

Happyplumber · 24 Jun 2010

Read the "frequently asked questions" it explains how to do these basic things

BenHarrison · 24 Jun 2010

I have a foot pump, so will check it tomorrow when I have more time and a fresh. I have the tap washer to fix too but I'm too hot and bothered now from this weather

So it's a leak somewhere, the Pressure alve leaking or the expansion vessel that is at fault

Axel · 25 Jun 2010

A footpump is not the tool - you need a mechanical 'pen' type pressure tyre pressure guage ideally, and a normal bicycle pump if it needs re-charging.

Remember to de-pressurise the water side of the system first!

Steve69the69Gas · 25 Jun 2010

Check all rad valves with caps off too

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Combi pressure drop every week

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