Me again! combi boiler pressure!

Postby justanovice » Sun May 13, 2007 4:36 pm

Hi again, thanks for your responses.
I have found a VERY small leak from one of the nut type things at the side of the top of one of my radiators (at the opposite side to where you would bleed it). Its not even a drip its just wet! Would this be a big enough 'leak' to be making my pressure go down on my boiler?
If so, how do I fix it? as it doesn't seem to be something you could actually replace... do I need a new radiator? Can I seal it with something?
Any advice gratefully received - many many thanks
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Simply Build It

Postby Paul Pepper » Sun May 13, 2007 5:09 pm

Simple job - turn off the radiator at BOTH valves, and get yourself something to catch water in. Open the bleed valve and catch the water until the pressure drops and no more water comes out. Go to the nut on the other end, put a cloth under it and undo it. Put PTFE or similar on the threads, wind it back in and tighten up. Close the bleed valve and open the radiator valves back up, bleed of any air and re-pressurise the system. Job done!
Paul Pepper
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Postby justanovice » Tue May 15, 2007 7:33 am

Thanks for that Paul - you make it sounds so simple - I'll see how difficult I can make it....!!!
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Postby justanovice » Tue May 15, 2007 7:37 am

Paul, do you think this tiny less than a drip can be the cause of my boiler losing pressure slowly but surely? or would you think there'll be a bigger leak somewhere else that I haven't yet found?

I'm hoping I can see light at the end of the tunnel here!
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Postby Paul Pepper » Tue May 15, 2007 7:16 pm

How much pressure loss are we talking about?
Paul Pepper
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Postby justanovice » Wed May 16, 2007 6:37 am

Well, if I keep the heating on constant then the pressure just drops about half a bar but its enough to affect my hot water. If I turn my heating off the pressure drops about a bar and a half and I certainly have no hot water then. Although the hot water is only mainly affected upstairs (rather than in the kitchen where the boiler is)
Sorry to be a pain - is it better to PM? I'm new to this forum business.
Cheers again.
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Joined: Thu May 10, 2007 5:31 pm

Postby Arnak » Wed May 16, 2007 9:25 am


I would assume from that pressure drop that there is a leak in the system somewhere, the problem is where?

I would have guessed that even with the pressure low the hot water should still work but I can't be sure of that as the pressure is normally only for the ch side of the boiler.

When was the boiler last serviced?

The lack of hot water could be a symptom of a fault in the boiler perhaps a temperature sensor?

Best to get a plumber to have a look.

No need to PM as these posts on the forum enable other folk to see what is happening and chip in if they can.

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Postby Paul Pepper » Wed May 16, 2007 6:08 pm

Just wondering how high you top the pressure up to - there's a pressure relief valve in the boiler set to 3bar. If you top up to 2bar or above when cold, the heat wil cause the pressure to rise and you'll lose it all to the pressure relief valve (dumps outside). Check that before you start paying plumbers.....

The lack of hot water upstairs would suggest that they may be a bit of a blockage in the domestic hot water heat exchanger. What boiler was it?
Paul Pepper
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Joined: Fri May 11, 2007 6:02 pm

Postby anothernovice » Fri Jun 08, 2007 8:51 pm

Please may I jump in on this? I had a new condenser boiler put in on May 1st. All singing all dancing, after clapped out back boiler. Pressure dropped dramatically after engineers left, system stopped working. Eventually (much later), water found leaking from small bathroom radiator (only two radiators in this minute flat; the other rad looks ok - I hope). So: new bathroom radiator put in last Saturday. BUT since then :oops: , pressure has dropped again, about four calibrations on the dial (just short of half a bar). SO....I worried like hell and today (Friday) had the boiler manufacturer's man in. HE says: Oh yes, that happens a lot with new boilers. Keep looking at it every week, fill up the pressure when it's low and after about 3 months it will settle down. Question: Was he just wanting to get away from a worrying woman on a Friday afternoon, or was he telling the truth? Call me paranoid...but I'm frightened I have a Leak Somewhere Under the Floor and the next thing will be having to rip the floor!!
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Postby htg engineer » Fri Jun 08, 2007 9:34 pm

He just wanted to get rid of you, pressure can drop a little after installation this is just any air in the system escaping through the auto air vent.

Depends on the size of the leak as to what action you should take, obviously finding the leak is the best option. If the leak is only small (pressure dropping over a long period) then leak sealer will solve the problem.

Do the obvious checks first and check all accessible connections ie on the boiler radiators and pipework for small leaks.

If only a small system and you go to the hassle of lifting floor boards, I would re-pipe the system, renew manifolds and radiator valves. if done correctly the pressure will not drop.

You tend to find that installing a pressurised sytem to existing pipework and radiators never really works.
htg engineer
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