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Discuss Loss of pressure when boiler is off in the Central Heating Forum area at PlumbersForums.net

Michael456

Messages
7
I’ve got a two year old alpha boiler, with 13 radiators running off it.

Ever since it was fitted there has been pressure issues, the more it’s on - the less problems.
But when the weather gets better and the boiler is used less the pressure is dripping every night to zero.

I’ve checked all the visible pipe work and cannot find any issues all the radiators seem to be bled correctly.

Also, I switched the flow and return valves off overnight after I’d set the pressure at 2.5bar, it lost no pressure but as soon as I opened the valves the pressure dropped down to one very quickly.

It’s driving me up the wall, gas engineers I speak to arnt interested in helping me coz it’s a crap awkward job.

I’m wandering could it be that I need an external expansion vessel because I’ve got so many radiators

It’s a large Victorian semi
Could this be my problem

Any help and advice would be very grateful

Cheers

Michael
 

ShaunCorbs

Staff member
S. Mod
Plumber
Gas Engineer
Messages
29,465
Solutions
1
You’ve tested the boiler and it held up pressure so it’s a system issue any pipework in concrete floors ?
 

Chuck

Esteemed
Messages
2,230
Just to be clear, you mean that the pressure indicated on a gauge is falling overnight not that the pressure relief valve outlet is dripping?
 

Michael456

Messages
7
Just to be clear, you mean that the pressure indicated on a gauge is falling overnight not that the pressure relief valve outlet is dripping?
I’ve checked the prv and the little pipe off the back of it is dry
 

Michael456

Messages
7
Just to be clear, you mean that the pressure indicated on a gauge is falling overnight not that the pressure relief valve outlet is dripping?
The pressure on the boiler remained at 2.5bar
Overnight when the flow and return valves were closed

as soon as I opened them the following morning
It dropped like a brick to 1.0bar
 

Chuck

Esteemed
Messages
2,230
The pressure on the boiler remained at 2.5bar
Overnight when the flow and return valves were closed

as soon as I opened them the following morning
It dropped like a brick to 1.0bar
Was the radiator system hot when everything was at 2.5 bar and you isolated the boiler? If so, there will be a rapid drop the following morning when you reconnect the boiler to the cold system.

Are you saying that you are having to keep adding water continually to the system to keep it running, i.e. there must be a leak from the radiator circuit and/or hot water cylinder?

You can test to see whether you need a larger expansion vessel by draining some water out of a radiator while leaving it's bleed nipple open. The idea is to get it half full of water with air trapped in the top half.

I think your problem is more likely to be a leak somewhere. The first step, obviously, is to have a careful look at everything to see if there are signs of damp / water / corrosion. Do this carefully because the next steps are harder work and/or a bit pricey.
 
Last edited:

Michael456

Messages
7
Was the radiator system hot when everything was at 2.5 bar and you isolated the boiler? If so, there will be a rapid drop the following morning when you reconnect the boiler to the cold system.

Are you saying that you are having to keep adding water continually to the system to keep it running, i.e. there must be a leak from the radiator circuit and/or hot water cylinder?

You can test to see whether you need a larger expansion vessel by draining some water out of a radiator while leaving it's bleed nipple open. The idea is to get it half full of water with air trapped in the top half.

I think your problem is more likely to be a leak somewhere. The first step, obviously, is to have a careful look at everything to see if there are signs of damp / water / corrosion. Do this carefully because the next steps are harder work and/or a bit pricey.
Hi
The boiler was cold when it was out to 2.5bar and then switched off.

every morning the pressure is zero

I keep looking for leaks and cannot find anything at all
No water marks
No drips
No wet carpets or wet plaster
 

SimonG

Esteemed
Plumber
Messages
20,392
Expansion vessel not big enough for system.

Have you taped a plastic bag or bottle over the pressure relief outlet?
 

hometech

Messages
126
dropping from high (2.5) to 1 is a big step but it might represent a very small volume of water. Once it has dropped from 2.5 to 1, if you leave it, does it drop again to zero?
 

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