Loss of pressure when boiler is off

[Michael456]

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]

You’ve tested the boiler and it held up pressure so it’s a system issue any pipework in concrete floors ?

 

[Michael456]

You’ve tested the boiler and it held up pressure so it’s a system issue any pipework in concrete floors ?

No
No solid floors
Only about 15ft of pipe work I can’t get to

 

[ShaunCorbs]

No
No solid floors
Only about 15ft of pipe work I can’t get to

I would if you could valve that part off and test overnight to see if it holds

 

[Chuck]

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]

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]

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]

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.

 

[Michael456]

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

 

[Chuck]

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

Does the system have a domestic hot water cylinder and, if so, what type?

 

[Michael456]

Does the system have a domestic hot water cylinder and, if so, what type?

No
Just a combo boiler

 

[SimonG]

13 radiators? How big are the radiators?

 

[Michael456]

13 radiators? How big are the radiators?

To be fair all different sizes

but most are bigger than 1200 doubles

 

[SimonG]

Expansion vessel not big enough for system.

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

 

[hometech]

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?