Heating problem advice

big_white_dog84 · 10 Feb 2013 at 12:26

Any heating experts in here?

I have a problem with my linea vokera 28 combi boiler losing pressure. For a while the pressure would shoot up when heating, then die to zero when heating switched off. The hot water would also cycle hot to cold when in the shower. I have cover with the aa and they came out and changed the expansion vessel and pressure relief valve. This solved the issue of the rise in pressure and the hot to cold fluctuation, but the pressure drop still happens. I can top it up to 1.5 bar and it holds there nicely for a long time, including having showers. It holds fine when the heating is on, but after I switch the heating off the pressure drops to almost zero over approx half an hour. Aa came back out and changed the pressure relief valve again ( some water leaking from outside pipe) and changed another part - a sort of barrel shaped brass component. However he left before he could see that the problem was still there.

Can anyone offer any advice before I get the aa out again and waste another half day off work?

I have checked all radiator fittings and no obvious leaks. Left tissue paper at all fittings overnight and all were dry in the morning.

Worst case scenario is a leak in the pipe under the kitchen floor as we have just spent a fortune on karndean flooring. I'm willing to change the boiler as long as I know that won't be a couple of thousand wasted.

Help?

big_white_dog84 · 11 Feb 2013 at 19:05

Thanks for the replies. If I had a leak then I would have thought the pressure would drop at all times, not just after the heating switches off. I could go through and top it up now and it would hold indefinitely until after the heating switches off next time.

big_white_dog84 · 11 Feb 2013 at 19:56

No drips any more since the aa changed the prv for the 2nd time. Pressure also no longer dying to zero, now stopping at about 0.2 which is a bit strange. When the heating comes on it rises itself to 1 and runs fine. Hot water cycling hot to cold sometime, but not all the time. Nightmare.

On the plus side I have had a look under the house and there seems to be a nice warren of crawl- space, so I now have a task for the weekend to get under there and look for leaks.

big_white_dog84 · 11 Feb 2013 at 21:32

Google has suggested the heating / expanding / leaking thing. In a way that makes it worse as it will be very difficult to find. I'm assuming if that was the case then the system is maintaining its own pressure when hot and it is only when switched off it loses its ability to compensate for the leak and the pressure drops until the system cools and contracts to stop the leak?

big_white_dog84 · 9 Mar 2013 at 09:08

Thought I should post the outcome, for anyone that is fussed.

Turns out it was a faulty pressure gauge. The pressure wasn't dropping at all. When I was topping it up to what I thought was 1.5 bar it was actually over 3, causing the prv to operate. Finally got this replaced yesterday and this morning was the first time I have woken up to pressure above 1 bar for months. Fingers crossed that's it. I have to say the aa were really good once they finally got their teeth into it - the problem was getting them interested in the first place.