combi boiler losing pressure

[ice cold]

Hi
I'm new to the forum so apologies if I've posted incorrectly. (if I have please let me Know.)

My combi boiler has started losing pressure. I noticed last night when I turned on the hot water tap, but the boiler didn't light. I filled the boiler via the filling loop to about 1 bar, but when I got home from work this afternoon I checked the boiler and the pressure had dropped to about 0.5 bar.
The boiler's a Main combi 24 HE, about 18 months old.

Before I call out a service engineer can anyone suggest a likely cause? I've checked the boiler, radiators and exposed pipework and can't find any sign of leaks.

If the best advice is to call out the engineer, is it okay to leave it until the new year, and just keep filling up the boiler?

Final question -the user guide for the boiler says to fill the boiler between 0.5 and 1 bar. I've read some threads in the forum which suggest up to 1.5 to 2 bar. What's best?

any advice appreciated.

 

[sonray ltd]

have you any pipework in solid floors etc ?
check the prv pipework that exits the external wall for leaks.
fill the system to about 1-1.5 bar

 

[rmbp]

Hello there, I had same problem couple of weeks back with a baxi. I changed the prv, problem solved. You should be able to check to see if its leaking by inspecting the external safety pipe, it doesn't have to be much of a leak to be a problem It might just be a drip.

 

[ice cold]

Thanks for suggestions re: prv's. I've checked the prv outlet pipe & it's got a small leak - about 1 drip every 35 seconds while the boiler is running. I haven't checked it yet when the boiler's off.Is this enough to lose pressure overnight? I filled it to 1.5 bar yesterday evening, got home today it was down to 0.9
As for the rest of the pipework it runs down a cavity from the attic to the first floor, branches off to bathroom & bedrooms, continues down to the cellar then back up to kitchen & living room. Most of the pipework is plastic (or PVC ?) so I don't think there are any hidden joints, and there's no sign of moisture on any pipework.

 

[Mike Jackson]

There's 2 possible problems here.

1. PRV is faulty or has some muck on the seat, If there is muck on the seat you may be able to clear it by operating it, if the seat is damaged you'll have to get it changed.

2. expansion vessel has lost it's charge pressure. You can tell this by looking at the pressure gauge when the system is running. There should normally be 1/4 - 1/2 bar rise as the system heats up, if it rises dramatically there is a problem with the expansion vessel. It either needs recharging or the diaphragm may have failed.

Mike

 

[ice cold]

Thanks for the suggestions Mike. The pressure seems fine at the moment - 1.0 cold, 1.5 with the boiler running, so the PRV seems the likely problem.

Senior moment! Then PRV drip mentioned in my previous post is actually from the condensate drain. (plumbing's not one of my strong points especially not gas boilers)

Is the PRV easy to check or should it be done by a Corgi plumber? - bear in mind my comment on the previous line!
If it does need replacing any idea of an approximate cost? Do Corgi plumbers usually charge a call-out fee, or just charge for the work done?

 

[townsmcp]

Ice Cold - did you get a reply about this? I have the same make and mdoel of boiler and the same problem - my boiler takes a week from topup to 2.5 bar to be drained down and cut off from working automatically (havent found any leaks anywhere) - the boiler is only about 18 months old also and a few months ago I already had to replace the air pressure switch - am considering taking out an extended warrenty and trying to get it fixed on that

James T

 

[sonray ltd]

2.5 bar is to high to start with.

 

[townsmcp]

The sticker on the unit itself says the pressure must be between 1 bar and 2.5 - most of the time I top it up to just under the 2.5 mark though so that I wont need to fill up so soon

James T

 

[sonray ltd]

if you top it up to 2.5 bar you'll have to be careful as the water expands if it reachs 3 bar it will activate the prv.

if it takes a week to drop it may not always be a visible leak.