help!!! boiler loses pressure when hot but fine when cold

[garyrus]

I’m new to this but i'm pulling my hair out and thought I would see if this works. I have a vokera compact 24 boiler (5 years old) and i'm having some bother with it. I will get up in the morning and the boiler will have cut off because after it’s last use it loses all pressure. I reset it and top up pressure to 1.5. heating comes on ok. Once its on it will stay on for as long as required. when it goes off it loses all pressure and dies. If i let the system cool down and top up again it will maintain pressure no problem so i've come to the theory that it only loses pressure after the heating goes off and the system is hot. I've had engineers out to charge the expansion vessel, problem persiss, now the engineer thinks its a prv and is ordering one in. does anyone know why it would keep pressure fine if there is no heat in the system but loses it all after use when its hot?

Checked all radiators and no sign of leaks

Any help appreciated, thanks

 

[muggles]

Have they charged the expansion vessel or changed it? I suspect if they've just tried recharging it it's actually split and you need a new one

 

[garyrus]

hi muggles, thanks for reply, they charged with a foot pump and said it was good for another 5 years. an engineer since refused to even check it after i told him the last guy charged it a bit

 

[spraggo]

I’m new to this but i'm pulling my hair out and thought I would see if this works. I have a vokera compact 24 boiler (5 years old) and i'm having some bother with it. I will get up in the morning and the boiler will have cut off because after it’s last use it loses all pressure. I reset it and top up pressure to 1.5. heating comes on ok. Once its on it will stay on for as long as required. when it goes off it loses all pressure and dies. If i let the system cool down and top up again it will maintain pressure no problem so i've come to the theory that it only loses pressure after the heating goes off and the system is hot. I've had engineers out to charge the expansion vessel, problem persiss, now the engineer thinks its a prv and is ordering one in. does anyone know why it would keep pressure fine if there is no heat in the system but loses it all after use when its hot?

Checked all radiators and no sign of leaks

Any help appreciated, thanks

It`s probably the shrieder valve leaking, the one that is used to pump the air in on the expansion vessel.

 

[garyrus]

I’m new to this but i'm pulling my hair out and thought I would see if this works. I have a vokera compact 24 boiler (5 years old) and i'm having some bother with it. I will get up in the morning and the boiler will have cut off because after it’s last use it loses all pressure. I reset it and top up pressure to 1.5. heating comes on ok. Once its on it will stay on for as long as required. when it goes off it loses all pressure and dies. If i let the system cool down and top up again it will maintain pressure no problem so i've come to the theory that it only loses pressure after the heating goes off and the system is hot. I've had engineers out to charge the expansion vessel, problem persiss, now the engineer thinks its a prv and is ordering one in. does anyone know why it would keep pressure fine if there is no heat in the system but loses it all after use when its hot?

Checked all radiators and no sign of leaks

Any help appreciated, thanks

It`s probably the shrieder valve leaking, the one that is used to pump the air in on the expansion vessel.

Hey spraggo, thanks for reply, is this an easy fix or anything i could try before they order in the prv?

 

[muggles]

Try pressing the pin in on the bicycle valve on the expansion vessel - if you get water in your eye it's broken. You may need to repressurise, especially if the valve is at the top, as the heating may lose pressure before the vessel fills up completely with water

 

[spraggo]

You can check the air pressure by using a ordinary tyre gauge, it should be about one bar, if not you can pump it up but you will have to relieve all the water peressure in the vessel first. Is the PVR leaking, if not why change it?.

 

[BingoBongo]

Don't understand why the wouldn't re check it.doubtful it's the prv if it's holding pressure when cold.maybe get a second opinion I've seen guys repressurising the vessel wrongly

 

[BingoBongo]

And I don't know anyone that can guarantee a vessel for 5 years after repressurising it.could last 5 days or 5 mins

 

[MANDATE]

sounds as though the expansion vessel has at some time lost some of its charge which has eventually resulted in the PRV opening at 3bar.
The PRV has then not fully sealed again, any dirt on the sealing face will result in a very minor leak and over night it will lose pressure without heating being on.
Setting the initial pressure to 1.5 bar means its going to achieve 2.5bar when heating is on.
It's essential the expansion vessel is operating correctly and never achieves the 3bar to operate the PRV.
Why not set the initial pressure to 1bar then note what pressure it rises to with heating on, and what pressure it drops back to with heating off.
My view is that the engineer has got it right and the PRV needs cleaning or better still replacing.