Losing pressure, and patience

[Kristaphwoar]

Hi all,
I posted here a while back about a horrible knocking noise from an old boiler system. One thing led to another and we actually ended up having a new system fitted. We now have a combi boiler installed in the attic (most of the pipes were up there any way).

It works a dream apart from one recurring issue, every 2-3 days I'm having to repressurise the system. I called the plumber back and his advice was to keep bleeding the radiators as he felt there was an air pocket in it, and eventually it would settle. I find that I usually only have to bleed one radiator in the en suite bathroom.

Regardless, we're still losing pressure and it's starting to drive me mad.

Any ideas? Thanks in advance.

 

[Iamchamps]

Look for a leak

 

[Kristaphwoar]

I have done, it's the first thing I did. There's no signs of a leak anywhere, no damp carpets or ceilings, and all the new pipes he put in are fine too.

 

[Poisonata]

The PRV (pressure release valve) is worth checking. If at any time it was activated during the install, sludge/metal sloughing from slowly corroding radiators can stick to the rubber washer and it fails to reseal perfectly. Where the PRV overflow exits your attic to the outside of your property there will be evidence of water escape. Either a slow drip or in the event the expansion vessel isn't correctly pressurised a dramatic rise in pressure when the heating is activated / hot water is ejected. Whilst an air pocket is credible especially when recharging a system after a complete drain down / consider also release of dissolved air after filling system fresh water, providing sufficient inhibitor has been added I'd have expected this to have resolved itself completely after a few weeks. How long has this been going on for / how much pressure are you losing every 2 to 3 days. The air is migrating to the highest point which I assume is your en suite radiator and will continue to do so with the constant reintroduction of fresh water. Consider seriously adding more inhibitor once resolved, you will thank yourself for it years down the line.
P.S. I'm not a plumber or qualified to advise you. Just have a general interest in all matters plumbing.

 

[dilalio]

Check PRV is not letting by first.
If it's up high and not accessible then disconnect it at the boiler and repipe into a bucket for testing period... If it's wet when you disconnect the pipe from the boiler, you will also know it has been letting by.
If it proved to be letting by then check the EV is properly charged (and correctly sized for your system).
Once that's been confirmed, continue to monitor PRV for let by and change that if it does.
If discharge from PRV is dry (or is dry once the above has been undertaken) then you need to start searching for leaks... Radiator valves and exposed pipework first. Then above ground floor staining and finally, if you have pipes under a suspended ground floor, it'll be lifting floorboards and inspecting .
You can also try, over-pressurise system when cold and listening at door thresholds... Common place for pipe punctures through floor covering installation.
Good luck... It's a common risk when pressurising a previously unpressurised system.

 

[ianmcd]

As @dilalio says, but dont be tempted to add any of the brands of leak sealer that are available, modern boilers do not like them, as already said this is very common when pressurizing an old system, most common is rad valves and they dont always show, as when the system gets hot the water evaporates, try ,when the system is cold take the pressure up and go round all the rad valves and see if you have a small weep, it doesnt take much for the pressure to drop on a boiler in a loft

 

[Gasguru]

Strange as it seems it's possible to have a leak on a sealed system AND draw air into the system at the same time.
Check the PRV as suggested and if no luck it's time to isolate the boiler...
Wait until the system (rads etc) is cold and at a stable pressure. Set the pressure to say 1 bar. Turn off the boiler power and isolate the flow and return pipework to the radiators using the valves under the boiler.
Leave it as long as possible..at least overnight. Then check the pressure to see if the drop is actually on the boiler (maybe on the heat exchanger although unlikely). Don't use the boiler whilst this check is done.
What boiler make and model?

 

[Kristaphwoar]

Hi all. Thanks for your responses and advice.
There's no dripping at all from the pipe outside, the radiator valves all seem fine both when it's hot and cold, and under pressure.

I 'think' I've just found a leak. It seems to be under the floor where the hot water tank was, and it must be a slow leak as it's only just started to show through the ceiling. Though it's a situation where I don't know if the stain is due to a new leak, or from something previous and I've only just noticed it because I'm paranoid (we've only been in the house since October). I'm going to cut a hole in the floor in the morning, if this is the source of the leak what would you recommend being my best course of action for a fix? It will be an 'old' pipe that the new boiler has been hooked up to.

Thanks