Gas smell from boiler after switching off CH

[Al@n]

Vaillant ecotec pro 28

Moved into a new property, yesterday we had the central heating on for a while, upon switching off the central heating within a few minutes we could smell gas.

When using the hot water it's perfectly fine.

Heating engineer has been out, serviced the boiler and replaced the flue and turret seals as they were slightly perished.

Gave the boiler a good sniff around and I think it's coming from the flue

Any ideas what would cause this?

 

[kidgreen61]

Possibly, the gas valve could be passing, needs checking sooner rather than later.

 

[Stuckinarut]

Could be the flue and could be products of combustion you're smelling. As above, get it sorted asap and I wouldn't use the boiler until checked

 

[oilhead]

Get your engineer back.

 

[Mister Banks]

Is the flue close to an air brick of fan vent?

 

[Al@n]

Is the flue close to an air brick of fan vent?

Nope

 

[Harry Bloomfield]

Gas valve passing, needs checked. You would not smell it, when it was burning, boiler in use, but a drop test should show it up.

 

[Al@n]

Gas valve passing, needs checked. You would not smell it, when it was burning, boiler in use, but a drop test should show it up.

It layman's terms what does that mean that the gas valve needs replacing or can it be repaired by replacing seals or something?

 

[Harry Bloomfield]

It layman's terms what does that mean that the gas valve needs replacing or can it be repaired by replacing seals or something?

With no heat demand, your gas valve should close up completely, if it doesn't, then it is permitting gas to still flow, filling your boiler with gas, plus the gas you can smell. If you have a Smart meter, with boiler off, and no gas appliances on, your meter will continue to record some gas use, when it shouldn't.

It usually means a new gas valve, but certainly not something you are allowed to do. You should not even be removing the cover, from the boiler, unless you are GS.

 

[Al@n]

With no heat demand, your gas valve should close up completely, if it doesn't, then it is permitting gas to still flow, filling your boiler with gas, plus the gas you can smell. If you have a Smart meter, with boiler off, and no gas appliances on, your meter will continue to record some gas use, when it shouldn't.

It usually means a new gas valve, but certainly not something you are allowed to do. You should not even be removing the cover, from the boiler, unless you are GS.

Apologies if this is a stupid question, why would the smell of gas only be present when the central heating is switched off but not be present when using HW or after the hot tap has been closed?

 

[Stuckinarut]

Apologies if this is a stupid question, why would the smell of gas only be present when the central heating is switched off but not be present when using HW or after the hot tap has been closed?

This is why it could be fumes/products of combustion. When using hot water, the fan is ramped up on maximum speed, whereas when using heating it's slower. I attend carbon monoxide alarm activations and have found this to be the case when running the boiler on a lower output. A recent intergas boiler had a similar problem - high fire was fine, low fire set the alarm off.

Imo, if it was the gas valve letting by, it should be evident on either. Again, wouldn't use the boiler until it's checked and sorted. Get your last engineer back.