Over-pressurising with filling loop disconected?

[Chris Taylor]

This one is driving me mad.


Water was dripping outside through the discharge pipe, so checked the boiler pressure guage and it was indicating 3.5 bar! Initially suspected the Pressure Reducing Valve. It was looking wet also. Pulled the cartridge out and it was in a bad shape internally. Fitted a new one after cleaning out the valve casing. Repressurised the system checking the external expansion vessel had 3.5 bar of air pressure inside, as stipulated. Pressure rose again to 3.5 bar inside the boiler without turning on the boiler (i.e. water still cold) !! Grrr


Next thing, is the small gate valve damaged through the filling loop as this was still connected? On disconnecting it, noticed that non-return valve was leaking slightly and some water exiting the boiler, but no sign of water passing the gate valve into the boiler. Changed the NRV anyway and fitted a new filling loop and gate valve as I had one.
Repressurised the boiler to 1.5 bar, shut the filling loop valve, disconnected the filling loop and pressure again rises slowly to 3.5 bar!! Grrr


Checked the boiler safety valve and this is functioning correctly. Quarter turn and it dumps water and pressure through the discharge pipe. Leave it to opperate normally and at 3 bar, it opens slightly releasing pressure to a drip, drip, drip outside through the discharge pipe.


So how can the system be repressurising with the filling loop disconnected? The mains pressure is higher than 3.5 bar if it can somehow enter the system, but how can it enter with the filling loop disconected?


Any advice appreciated.
Chris

Edit. The boiler is a Vaillant Thermocompact VU GB 282-5

 

[ShaunCorbs]

domestic or commercial, as commercial normally have an automatic filling loop?

 

[kris]

Is the heating on when the pressure is rising or is it off, the only thing I can think of is a crack inside the ;()£:/-/:; ,,best to get a qualified gas engineer round to diagnose the fault,,,

 

[Chris Taylor]

Thanks,

Crack in the?

No, heating system can be on or off, it makes no difference!

Very few places where both the closed heating circuit is in in contact with the hot and cold water tap circuit.

Only by isolating the high pressure feed, does the pressure fall gradually on it's own.

It's a domestic system.

 

[townfanjon]

Chris, its forum rules, we wont give out any info what might mean you remove the boiler case , sorry

 

[drip-dry]

This is not a boiler problem but still would advise you pass this over to someone who knows what they are doing as an un-vented cylinder

 

[Chris Taylor]

I agree that this is unlikely to be a boiler problem and certainly nothing gas related. I am a Royal Air Force Airframes Engineer responsible for high pressure aircraft hydraulics and the idea of paying many hundreds of pounds in labour charges for someone to change a valve, cylinder etc. when it is something I can do myself makes no sense. I just need to diagnose the fault and I can do the rest.

 

[Chalked]

Get somone in. It's not the boiler. The Vaillant cylinder is a enamel lined steel cylinder. This will need replacing by a G3 registered engineer.

 

[ShaunCorbs]

I agree that this is unlikely to be a boiler problem and certainly nothing gas related. I am a Royal Air Force Airframes Engineer responsible for high pressure aircraft hydraulics and the idea of paying many hundreds of pounds in labour charges for someone to change a valve, cylinder etc. when it is something I can do myself makes no sense. I just need to diagnose the fault and I can do the rest.

sorry to say if you cant diagnose the fault the you shouldn't fit it/ repair it

each to there own trade

 

[Chalked]

You probably are skilful enough to replace what is wrong. But you can't buy that cylinder anymore.
If you don't know what is wrong and have To ask on here. Plus you are legally not allowed to. Your insurance will take a dim Veiw if there is a problem.

The whole job should not take more than half a day.

 

[PlumbBobBob]

This plumbing forum will not provide advice to anybody with regards to boiler repairs or any other form of gas plumbing without you first providing us with your Gas Safe Registration number in a thread - for very obvious reasons. If you're not qualified to touch gas, you should stay well clear of trying to!