Leaking Pressurised Central Heating System

Richard081274 · 25 Nov 2010

I am looking for a bit of help and guidance on a problem with my central heating system. The pressure is dropping by about 1bar over a 24hr period. Also the pressure has started going into the 'RED' around 3bar when hot after the system has been pressurised to 1.5bar when cold. It only started doing this around the same time as we noticed the pressure loss. Had an engineering take a look when he came to do the annual service, but he found no problems on the boiler and could see no leaks on any accessible pipework. He asked me to put a container under the Pressure relief pipe outside to see if it collects water, but he thinks I likely have a leak below the floorboards. I asked about using a leak sealer, but his experience was that this wouldn't work, but I would appreciate a second opinion.

Thanks for any advice you can give.

45yearsagasman · 25 Nov 2010

I would suggest that you check the expansion vessel precharge.Its very difficult when no boiler/system details are given to give accurate advice 1st time.Come back.

Richard081274 · 25 Nov 2010

Thanks for the reply. The boiler is a Baxi Duo-Tec Combi 28 HE and nearly 4 years old. The pipework has microbore pipes going to the radiators from a central larger pipe, though above the floorboards connecting to the radiators they are 15mm pipes - don't ask me why it was like that when we bought the house.

Hope this helps.

craig51 · 25 Nov 2010

As above, most likly the expansion vessel needs recharged/replaced. Im pretty sure there is a sticky somewhere about it.

To check quickly, go outside and see if there is water coming out of the prv, stick your pinky up inside it to see if its wet.

Also, if you know how to, if you let some air out of the expansion vessel but water comes out instead, its burst. If no water comes out, then its probally needs recharged!!!

Richard081274 · 25 Nov 2010

Thanks for the reply. The engineer yesterday checked the prv pipe and said it was dry, but I did check myself this evening and it was wet, though not dripping. I have placed a jar underneath it to see if there is a flow of water from the pipe at some point.
Don't know if it helps, but the system loses pressure through the course of the day. I set it to 1.5bar in the morning when it is cold, then it switches on for 3 hours, then I check it a couple of hours after this and it is down to about 1.25bar. Follow this through the day (the heating is on for 9 hours in 3 x 3 hour sections between 6am to 9pm) until the following morning and the pressure is around 0.5 bar or sometimes less so the low pressure code is flashing.
It might be a stupid question, but wouldn't the engineer have checked the expansion vessel durng the annual service?
Thanks

craig51 · 25 Nov 2010

It will only pass when the heating is on!!!! and when it does it will be a trickle. The jar is a good idea.

Most RGis dont check the expansion vessel when servicing, just the pressure on the gauge and watch how it behaves!!!

Richard081274 · 25 Nov 2010

Thanks, I will call the engineer and ask if he checked the expansion vessel or not.

If he did and it was OK, any other ideas? What about leak sealers like Fernox, would this work if it was a leak dropping 1 bar in 24hrs?

Thanks

Wangerman · 25 Nov 2010

Richard081274 said:
Thanks, I will call the engineer and ask if he checked the expansion vessel or not.

If he did and it was OK, any other ideas? What about leak sealers like Fernox, would this work if it was a leak dropping 1 bar in 24hrs?

Thanks

I suppose it depends on the size of the leak and the size of the system.

One bar pressure drop in a small install in a flat could be not more than a drip over time. one bar pressure drop in a 6 bedroom three storey house will be substantially more.

craig51 · 25 Nov 2010

OK, lets assume you collect no water from the PRV ( i bet you do, considering the pressure is rising to 3bar then dropping).

The only other option is a leak somewhere.

If you did have a leak, first would be to find it by all means first. Check with your hands are all joints possible, and you may need to lift floor boards.

IMO, leak sealer is a last resort, as it can screw some boilers up!!!

End of the day, what you described as per your first post is a classic exp ves issue. Some would say it might eb the prv valve not seating properly, therefore allowing it to drop, but this wouldnt explain why it was going to 3 bar first!!!!

libby lou lou · 25 Nov 2010

Prv, guess, as 3 bar pressure in leaky pipe work wouldn't let the valve go off?

Axel · 25 Nov 2010

libby lou lou said:
Prv, guess, as 3 bar pressure in leaky pipe work wouldn't let the valve go off?

The prv is designed to open at 3bar, so it's the fact that it's getting to 3 bar in the first place that is the problem = expansion vessel issue.

onwards · 26 Nov 2010

I had the same issue with my pressurised system.
In my case, yes water was leaking out but only because of the raised pressure during heating. The raised pressure was being caused by the non-functioning pressure vessel.
I fixed it with a foot pump.
De-pressurise the tank. Find the charge nipple, mine was on the bottom. I attached the foot pump and noted tha the pressure was negligible so I pumped it up. TBH I can't remember what pressure I pumped it to. I found the advice on here somewhere so a search on here might help....
Once I had re-charged the vessel and re-pressurised the system to 1 bar, the water pressure only rose by .5 bar during heating and no more water was lost...
ATB

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Leaking Pressurised Central Heating System

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