Unvented heating system, unusual boiler fault

[Pauld1962]

Called to a customer today and the system boiler keeps repressurising on its own ... After I dropped out all the pressure I watched as it refilled ... The filling loop was disconnected at the time ... Customer reports that it's never done it before ... The only way I could stop it was to turn off the cold mains ... !! ... Any help appreciated ..

 

[ShaunCorbs]

Combi boiler ?

 

[townfanjon]

Says system but maybe combi

 

[Scott_D]

Old filling loop somewhere

 

[chris watkins]

Can only be from where the mains & heating water are separated by a connection or surface which is leaking.
System boiler = coil on unvented cylinder
Combi boiler = plate heat ex

 

[Chalked]

Split coil ?

 

[Pauld1962]

It's an old system boiler Vaillant thermocompact vu 282/1e ... Unvented cylinder ... Is there a test for split coil and what causes it ... They use the immersion most of the time as solar power is available ..

 

[Best]

If you can isolate only the water going to the unvented cylinder, that will prove if it is the fault

 

[chris watkins]

If you can isolate only the water going to the unvented cylinder, that will prove if it is the fault

or isolate F&R to Cylinder coil.

 

[Best]

or isolate F&R to Cylinder coil.

I hadn’t thought of that!
And if I had installed the unvented cylinder, there would be a gatevalve on the return.

 

[Pauld1962]

I isolated the F&R at the boiler at 1.5bar and it held ...... Once the return was opened the pressure rose immediately and water meter was turning over ...

 

[chris watkins]

Drain & valve off cylinder coil in that way they can still use the immersion or Solar for domestic hot water.
The heating system pressure should stop rising. If so it is the coil & you will have to order a new cylinder.

 

[Best]

I isolated the F&R at the boiler at 1.5bar and it held .. Once the return was opened the pressure rose immediately and water meter was turning over .

Probably cylinder coil gone then.
Is it a copper unvented cylinder, or stainless steel?
If you are not G3 qualified, just be aware if no isolating valve on mains supply to unvented cylinder, then only install one BEFORE the combination valve. (Between the combination valve and cylinder must not have any valve)

 

[Pauld1962]

Thanks for all your input / answers guys I am going to call back to the customer and inform him ... That'll be fun ...!! .... Thanks again gents ...

 

[Pauld1962]

Apologies "Best" .... It's a stainless steel cylinder ...