Smell of gas near boiler

Albermarle

Our boiler is in a large cupboard in a first floor room ( in a house). The heating was on for around half an hour this lunchtime and afterwards there was a smell in the room. To me it smelt more like combustion fumes than gas. Opened the window and it soon cleared. Put the heating back on and this time smelt more like gas than fumes.
Anyway have switched off the boiler at the main switch, and switched off the gas for the house at the meter.
Gas safe guy coming tomorrow, but just wanted any hints what it likely could be.
System boiler - WB greenstar - about 6 years old, serviced a few months ago.
Thanks

ThisIsWeird

There clearly shouldn't be any fumy smells in the room. So, it must be coming from somewhere.
You have windows in that room, so any chance the trickle vents are open, and the wind moving in a direction which could be drawing air in these vents from anywhere near the flue terminal?
Failing that, could it be that the test terminal cap has fallen off (as it did to my Glowworm when it turned into plastic crumbs)? Have a look at where the flue exits the top of the boiler - can you see a wee screw-on cap there, or the absence of one?
Another possibility is that the fumes are getting in from under whatever is above the terminal - soffits, tiles/slates etc, but that would be unusual.
When our boiler fires up and I'm outside near the flue's location, there is usually a very brief whiff of unburnt gas smell, so clearly some is expelled before the burner fires up fully. So the fact you sometimes also smell unburnt gas is no great surprise, and doesn't necessarily suggest a separate issue, or leak. So, likely it's all exhaust-gas related.
All you can really check, I'd suggest, is that wee test spigot. Having said that, ours had been missing for months with no noticeable smells - the cap was so broken down, I didn't recognise it...)

Albermarle

Older double glazing - no trickle vents- window was closed.
Not windy today.
Test terminal cap intact.
Normally no smell at all until it happened today, so I am assuming something must have broken/cracked and is letting fumes ( and maybe unburnt gas ) escape.

Silvertabby

Tomorrow!  When taking a meter reading from our outside meter we caught a definite whiff of gas.  British Gas were with us within the hour, and found a cracked pipe within the meter box.

This wasn't over Christmas, but their emergency cover includes weekends and all Bank Holidays.

ThisIsWeird

Albermarle said:

Older double glazing - no trickle vents- window was closed.
Not windy today.
Test terminal cap intact.
Normally no smell at all until it happened today, so I am assuming something must have broken/cracked and is letting fumes ( and maybe unburnt gas ) escape.

That's really as much as you can check. So I'd go 'Silvertabby' on this.

FreeBear

Silvertabby said:

Tomorrow!  When taking a meter reading from our outside meter we caught a definite whiff of gas.  British Gas were with us within the hour, and found a cracked pipe within the meter box.

This wasn't over Christmas, but their emergency cover includes weekends and all Bank Holidays.

The gas distribution company (Cadnet in my area) is on call 24/7 including weekends and public holidays, and the will be out immediately if a gas leak is reported.

If you smell gas, don't take any chances. Just call the National Gas Emergency Service immediately on 0800 111 999 and let them deal with it.

Cherryfudge

Gas Emergency come out at all hours - We've had them in the middle of the night during a storm, bless them. It's what they're paid for, so don't hesitate to ask for them ASAP.

If there are gases you can smell, there may also be carbon monoxide, which is deadly and which you can't smell - so keep your house ventilated, and get out if you have the option. Better safe than sorry.

John_the_Boy

Not saying it is this but it is possible to get a smell of gas/combustion fumes from the casing of your boiler.

I had this when we had a new WB fitted and the wife could smell 'gas' not long after the boiler went off. Took ages to get resolved and had Cadent out 6 times. In the end WB came out and admitted that what we could smell was permitted leakage from the boiler case folds.

https://registeredgasengineer.co.uk/technical/technical-bulletin-151-combustion-box-leakage-rates-on-worcester-greenstar-gas-boilers/

Just don't take risks and get Cadent out in the first instance.

Albermarle

John_the_Boy said:

Not saying it is this but it is possible to get a smell of gas/combustion fumes from the casing of your boiler.

I had this when we had a new WB fitted and the wife could smell 'gas' not long after the boiler went off. Took ages to get resolved and had Cadent out 6 times. In the end WB came out and admitted that what we could smell was permitted leakage from the boiler case folds.

https://registeredgasengineer.co.uk/technical/technical-bulletin-151-combustion-box-leakage-rates-on-worcester-greenstar-gas-boilers/

Just don't take risks and get Cadent out in the first instance.

Everything has been checked.
No gas leak and boiler has been fully checked by a Gas Safe Engineer. It is running fine and no sign of any smell or any issues with combustion, flue gases etc.
So could well be the issue highlighted in the link you sent, as the smell was a mixture of gas and combustion products and it was noticeable after the heating had gone off but quickly dispersed.
The question now is if that is the reason, why has it never happened before, or at least never been detected before. Strange but does seem the most likely explanation, so thanks for that.