Condensing Combi losing pressure

[Fusion]

Morning all

I wonder if you could possibly advise on a problem I have with my recently fitted Baxi Platinum cond/cobi boiler.
It was professionally fitted in November 2008 and is still under warranty. The pressure was lost the next day after handover, and before re-pressurising the system, I consulted with the installers who said it was not unusual for this to happen as there could still be air in the system.

My problem is that the pressure only stays at 1.5 Bar for an average (taken over 4 months) of 30 days. The pressure progressively drops over this time. I have contacted the installers who have been out to investigate and thoroughly checked for leaks on 'their' plumbing and the boiler and can't find a fault.
I appreciate, as they have confirmed, that a leak may be under the floor boards in existing pipe work and I would have to take up floor boards to investigate at my own cost. This I understand as existing pipe work was not in 'their' remit.

However, now that the warmer weather is here, the heating is turned off and the system pressure is rock steady on 1.5 Bar over 30 days. This suggests a boiler 'problem' to me. Would you not agree?

Have any of you guys come across this issue before and is it a common problem?

I'm aware that I or any plumber/heating engineer can't actually investigate 'too' far into the boiler because of the warranty in force.

Any replies/advice gratefully received.

 

[jonathanb]

Was the previous system a sealed pressurised system (combi)or have they converted an open vented system (traditional tanks and cylinder) using the existing pipe work? If it is a conversion then it IS the installers problem as not just his pipe work but also the existing to what he's joined onto and put under pressure. Often valves and fittings leak when changing over to a sealed system and would explain the pressure drop - check compression fittings and rad valves and tails, as often the culprits, a small leak over time will do this. Any pipe work under concrete floors as thats another favourite? I think your installer should have had a good check of all installation pipework to be fair as every now and again this crops up and all part of the job in my eyes, maybe i'm too soft!

Threre have been some boilers in the Baxi range which have had leaks internally in the plate heat exchanger with the leak not visable or aparent as escapes through the condensate drain - check for discharge when boiler off. Also check the pressure relief valve (usually located on outside wall / 15mm copper pipe) any evidence of water discharge from this could also be the problem.

Think you've got a leak on the system though, as you say pressure stabilised with heating off. Sometimes leaks only happen when system on and hot / pump running and stop when all cooled and not in use, so get it cranked up to full and get those floorboards up and see if you can find problem first. Otherwise Baxi Heat Team as under warranty to sort any problems with boiler.

Good luck!

 

[Fusion]

Thanks for your reply.

Yes the previous system was traditional tanks and cylinder. I did forget to mention that new radiators and valves in every room were fitted so initial leak checking was easier.

I don't appear to have a drip on the relief valve and have checked that weekly over the last 4 months.

I appreciate the expansion and contraction on the pipework when the pipes are hot will open/close leaks so your advice on cranking up to full heat will confirm the issue. I'll have a go later in the week and will have to use the timer to allow the system to work over a period of days to get a better idea of what's happening with the pressure. The property is a bungalow fortunately with no concrete floors in the equation.

I did phone the Baxi warranty people up a few weeks ago regarding the use of a sealant in the system to plug any minor leaks, but was told from the outset, the warranty won't cover any foreign bodies in the system.

Thanks again for your help.

 

[Puddle]

When you say there is a presure drop,how much,a what presure do you top the system up ie when you see it at 1.3bar,1 bar,1/2 bar ?
I ask this so we can gauge the extent of leak and presure drop,do you top boiler up when cold or hot

 

[Fusion]

Thanks for your input Puddle

I top the system pressure when the hotwater/central heating has stopped working. As you know most modern boilers 'cut out' to prevent damage when there is a pressure loss. My Baxi, as a I assume all new Baxi's, is set to 'cut out' at 1 Bar.

When say there's no hot water, I know the pressure has dropped to 1 BAR. I top up to 1.5 BAR. I can't guarantee the exact pressure is applied each time I top up, as I don't know if the gauge has been specifically calibrated. But I use the 1.5 mark to go by.

We can take it that the system loses 0.5 BAR over 30 days on average when the heating is on. If it is a hidden leak as it probably is, it obviously isn't a seriously one and perhaps the leak evaporates due to the very hot pipe(s).

 

[bunny78]

maybe something on the heating pipework I would of said valves if these were the originals maybe a compression fitting weeping slightly on expansion/contraction when the heating is on is the rad pipework "microbore 8/12mm? could be on the manifold deppending which type it is?
Last resort maybe a leak sealer put in to the heating side might help BUT might invalidate any warrenties on the heat exchanger.
Needs sorting really as your introducing fresh water most of the time which will over time speed up breakdown/sludge in your heating sysem.
Awkward one for your plumber as he cant inspect all the heating pipework so cant 100% say it wouldnt leak when the new system was fitted.

 

[rob jefkins]

Sounds to me either a leaky rad valve or dodgy joint within the heating pipework system. Hopefully you can sort it without lifting floorboards.
Good luck

 

[ericp]

I have a similar problem with a Worcester Greenstar Heatslave 18/25. I've read all the related threads but need some clarification on the PRV/Expansion Tank issue.

If I leave the sytem running contiuously, pressure stays up at 1.5 to 2.0 bars for a week no problem. If however, I run it on the timer, I have to get up at 6.00 am every morning to repressurise the system which by then is down to zero. It then runs fine all day at around 1.5 to 2.0 bars. (I pressurise to about 1.0 bar when cold). If I don't fill it up, the system starts up, air seems to get into the pump (how?) and after a while the overheat cut out operates. In the past I was releasing steam from the end screw on the pump but have stopped that by re-pressurising before it occurs.

There is some evidence of a leak in the prv - I put a freezer bag over the outlet and when working normally I can get about a cupful of water in 24 hours. When switched off however, a pint or so collects in the bag.

The boiler is relatively new (2-3 years?) and been regularly serviced. The guy who serviced it a couple of weeks ago reckons it may need a secondary expansion tank since the house is quite large, but since the pressure does not go above 2.5 bars when hot (that's what the handbook says), I'm not sure this is the root of the problem. The other parameter in the book is if the system is bigger than 180 litres which I don't think it is.

I have tried letting off the pressure using the prv to try and flush out any dirt, but looking at previous posts, this may have made matters worse with dirt getting stuck.

If someone can help me understand why the loss of pressure is happening when cold and why air gets in when the system cools down that would be a step forward.

There are no leaks visible in the rads or pipework (microbore - horrible I know but that what the guy installed and it seems to work).

The engineer checked the expansion tank simply by pressing the valve to check air came out and not water. He didn't check the actual pressure so I am going to try that next. However I'm not sure what to pump it up to. The installation manual quotes initial charge pressure of 0.5bar for a 180 or 107 litre system (initial system pressure of 0.5 and 1.0 bar respectively) but 1.0 bar for both system and charge pressure for a 138 litre system.

I don't know the capacity of my system but there are 12 rads plus a towel rail fitted.

Regds

EricP

 

[CharterGAS]

expansion vessel in the boiler is too small, a quick calculation is 1 L expansion for every radiator. If you have more than 8 rads you need secondary expansion vessel as suited to system

 

[ericp]

Many thanks - that makes sense.

Best Regds

Eric