Over-pressure on CH, but expansion tanks fine and related to unvented tank

[Iain24]

Not looking to fix this myself but could do with some insight as to what’s wrong…due to sell the house on a few weeks and not comfortable doing that without this being fixed.

CH pressure getting up to 4-5 bar and pressure relaxing through the 3 bar pressure relief valve. Connected to unvented tank.

Both expansion tanks (tank and CH) correctly pressurised and replaced earlier this year.
When I isolate the mains feed to the unvented tank, the pressure in the CH system drops back to 1.5 bar.

Filling loop disconnected during all this time. How is the CH system seeing this pressure?

am I likely to need a new tank or is it a valve issue?

Like I say, I won’t be doing it myself, just need to get it fixed.

Thanks.

 

[SJB060685]

Sounds like a split in the cylinder coil. If it is its new cylinder time. Having said that the pressure should be regulated to 3 bar on cold fill to cylinder.

 

[exedon2]

Would agree coil gone not common but it happens!

 

[Timmy D]

With the cylinder cold feed isolated, run a hot tap, does the boiler pressure drop?