DIY Doctor UK DIY Forums

Hi, I have a glow-worm 18si boiler and the pressure keeps dropping to 0.6. I had it serviced and this still happens, only when the the heating is on plus water is going straight out the overflow. The service people said we have a water leak somewhere but no sign of any, no damp marks or drips. Tried everything can anyone help?

Hi,

If water is escaping out of the PRV (pressure relief valve) then your prv might not be seating correctly or diaphragm in pressure vessel problem?
I suggest you get a better RGI.

Hth

Hi Steve,
Thanks for the swift reply. When we got the guy out to service he fitted a gas filter and a PRV. but we still have same problem, he told us we must have a water leak somewhere. But we cant find it. What is a RGI?
Hil

If the PRV is ok, and the pressure never rises and discharges via the PRV. then it probably is a leak somewhere on the system.

htg

Hi htg,
We searched all over and cant find a leak anywhere.
We did have a new copper cylinder fitted( because the old one was leaking) but the problem is worse and the pressure drops quicker each day. We have to keep checking to see if red light flashing 0.6 on the boiler everytime the heating comes on. Tried to get the firm who installed gas 3 years ago but they are out of business. Had another firm and they say about leak but still cant find it.
The pressure never rises and only discharges through the overflow out the side of the house.

The pressure never rises and only discharges through the overflow out the side of the house. ?????

Is does discharge outside ?

htg

Hi
Sorry I might have said the the wrong thing. The water is going through the PRV and discharges water out the side of the house. I said overflow before but appearently our overflow is in the roofspace.

Hil

RGI - Registered Gas Installer

Ok, if the pressure doesn't rise but water is escaping via PRV. The PRV needs replacing.

If there is no water coming from PRV, and the system is losing pressure then there's a leak somewhere.

htg

Hi htp,
If we have the hot water on the pressure is fine. Once we put the heating on the pressure drops. We were away 3 weeks and only hot water left on everything was the same as we left it.
We had RGI out in April this year,told them the problem and they replaced the PRVand gas filter,but still same problem. We had RGI back again ,then they said about a leak, but looked everywhere, no leak.
We haven't used the heating all summer but now the time has come to use it.

Tonight we had a plumber out and he couldn't find the leak. We explained what was happening and done the following to show him.

Heat on after 15mins,temperature up that opens PRV which starts to drip water outside house. We then turned the themostat down from 30c to 16c which turned the boiler off. After 15mins we turned it up from 16c to 25c, a gush of water shot out via PRV outside house. So then the red light was flashing on the boiler. So we topped up to 1.0 turned heat on, temp started to rise, next the PRV opened and another gush of water outside the house.
Plumber has told us to get RGI back again. So phone call tomorrow. The RGI we had in April has good repution and gas installer of the year awards.

Hil

As i said before if the pressure DOES NOT rise - it's the PRV at fault.


htg

Hi

probably a bit late but I have an idea...

It could be a problem with the actual pressure gauge.

Sometimes this problem occurs by over pressurisation during the water commissioning of the boiler and can result in pressure loss through the PRV.

Maybe get your RGI (!!) to check that out??

AH.

Hi
We had trouble trying to get the RGI back outagain. Still waiting on them. Anyhow now we have had Phoneix Gas out explained everything to them about the PRV etc. and they talked about expansion tank(we havent a clue) they have "drained the boiler and unblocked hose,charged vessel to 1.0bar and pressurised to 1.4bar ,checked opeartion of c/h+h/w controls all ok and left working", as written on their report.
Any of this make any sense to anyone?

Yes, that's why i was asking if the pressure rises when the hot water or heating is used. If the pressure was rising then it points to a fault with the expansion vessel. They can sometimes be re-pressurised (as this company has done) or you need to replace the expansion vessel.

The expansion/pressure vessel is a drum with a rubber diaphragm right down the middle. One side full of air - the other side will be full of water when the heating system is full. When the heating or water is on there's expansion in the system, this expansion is taken up through the diaphragm by the air (as air compresses easier than water).

If the diaphragm splits the expansion in the system has nowhere to go, and builds up in the boiler/system - when the system pressure reaches 3.0 - 4.0bar a safety device called the pressure relief valve is operated, the excess pressure will be discharged outside, normally via a 15mm copper pipe.

Hope this makes sense.


htg

i have had a similar problem when the pressure kept going down the British Gas engineer finally replaced a valve in the boiler that was leaking. This solved the problem for about 8 months and the pressure has gone down again but no water leaking out anywhere.

I repressurised back to 1 bar but for some reason is now showing 2.4-2.8 bar on the megaflow tank and also the boiler display is flashing at 2.8. has been like this for a few days.

Can anyone advise how i can reduce the pressure back to 1 bar?