A year on & still losing pressure overnight...

[VikkiN]

I'll try to be brief.
Ideal combi boiler, 9 yrs old. Usually on timed heating. Starting losing pressure o/n last autumn. My contractor back and forth over winter, no obvious leaks to pipes, replaced virtually whole boiler. I said afterwards "I expect I should think about replacing it, quite old now". He laughed and said not to do that, with all its new parts it was virtually new anyway. It seemed ok, then we switched off heating for summer. All's been well.
There one section of pipe in concrete floor. All bar a straight run of 10ft was replaced this summer as having some other work done. No leaks found.
Put heating back onto timer this week - same old, same old. Go to bed, get up at 6am, boiler dead as a dodo, pressure zero. Put some pressure back in, works fine all day. Go to bed....
Any suggestions/ideas/freaky observations welcomed. I am truly at the end of my tether and contemplating the sledge hammer.

 

[Alfredo]

Whenever I hear the words 'Pipe in concrete floor' I shudder a bit as its often where the problem lies. You have two options.

1) Inject Fernox leak sealant into the system. It will either work or it won't, but a system that loses pressure over night suggests a leak that sealant might not be capable of coping with, or it suggests a pipe with multiple pinholing. All the same, for what it costs I'd give it a go and see if it makes any difference.

2) 2nd and long term solution is to repipe on a drop. Thats a bit more costly, but usually the right way to go.

Are you sure water is not coming out of the PRV when the system is running and hot. If so it could be the pressure vessel with no pressure in it, or a failed diaphragm in the pv. It would run fine all evening, then when you turn it off and it cools down overnight, the water contracts, all the pressure goes and it won't fire next day. Worth checking if you havn't already.

Alfredo

 

[MANDATE]

I would be inclined to check the expansion vessel along with the pressure relief valve.
The expansion vessel would have been 'air' charged when it was installed and like car tyres, the pressure drops over a period.
You have to make sure there is no water in the vessel when you pump it back up to about 0.8bar.
If the vessel is full or partially full of water instead of air the extra volume of water created when heated will have nowhere to expand to. This leaves only one other action. It is forced out through the pressure relief valve.
This releases the pressure and will need to be topped up again, but once the relief valve has been opened it tends to get dirt trapped on the sealing faces when closing, so you seldom get a good seal. So you now get a small leak.
You then find it easier to replace the valve as against cleaning it.
You could start by securing a plastic bag on the pressure relief valve outlet pipe and leave it overnight to see if it catches any water.
Also take note the rise in pressure when putting on the heating. The rise should be around 1 to 1.5 bar, anything more than this indicates a expansion vessel problem.

 

[spyke749]

Not a plumber, just a reasonable DIY'er, so, my advice is only from my own experience.

My system did just as yours, it was a leaking auto breather valve on the top of the boiler.

I had swapped a rad for a heated towel rad, lost pressure in the system etc etc When I refilled the system, auto vent valve operated, let the trapped air out, but, would not seal correctly. Hence I lost a cup full of water over night that tended to evaporate off the top of the boiler housing, pressure would drop, hence no boiler in the morning.

Replacement part was £13 from Plumb Center, 10 min job to swap.

 

[rojaca]

why did your installer not attempt to isolate where the drop was occuring before replacing expensive parts?
would it not be easier to isolate the relevant parts if the circuit first and see if the problem persists?

 

[VikkiN]

Thank you all. I will run the system on the timer this weekend (certainly chilly enough here for it) and see how it goes. Will get out where the pressure relief pipe is tomorrow and rig up something to see if anything's coming out while system's running.
My contractor is on a yearly fee (guess who) and to be honest I find they just want to rush in, fit a new such-and-such and run out again - they don't want to get too involved in tracking down any leaks under floorboards etc - not cost effective I suppose.
I had even considered getting in one of those companies who do the thermal imaging to check the section of pipe that wasn't replaced this year.
As soon as I put some pressure back in, everything fires up and it's fine again, so things could be worse....

 

[MANDATE]

I think you will find the auto air valve mentioned by spyke has a loose fitting cap to allow air to escape. Now for testing purposes this cap could be closed which would stop any leak from it.

 

[ChrisR]

Which Ideal Combi?
If it's a Response it's normal sir, they often do that in the latter stages of their life.
They lose water through the heat exchanger until they're too wet inside it to light.