Gas smell on ideal RS 50 boiler

26 Nov 2023
Reaction score
United Kingdom
Recently noticed a gas smell coming from my ideal classic RS50 boiler. Cadent have been out and confirmed a small leak and capped off the gas. The question I have though is that the gas smell only appears when the boiler fires up not when the pilot is burning normally. Gas smell continues as boiler burns higher. Any advice on what it could be? I thought it may be a faulty gas valve. Engineer is coming out tomorrow but I’m just curious as to what people think.
Sponsored Links
If the gas smell only happens after the boiler fires up its after the gas valve, so a drop test won't show it (unless the gas valve is passing). Could be a few things and any RGI would know what to check. Its not something you can do yourself so get a second opinion. If you're worried i would turn it off at the mains, if its a "gas leak" get the gas transporter out and say you can smell gas but if they find a leak they will turn it off (safety first). Dont use your boiler until problem is fixed.
Btw, most boilers will have an unburnt gas smell coming from the flue upon ignition so to rule that out close the windows/
Thanks @HandyMan23 the gas is now off at the boiler. Gas safe engineer coming tomorrow . Smell of gas is only when the boiler is fired up when it returns to normal idle low pilot flame there’s no smell, just wondered what kind of things could be causing it.
Sponsored Links
Right, I will get them to check that @HandyMan23 . The smell only seems to be coming from the left hand side of the boiler in this area that’s why I thought it could be the gas valve leaking when more gas is put into the burner


  • IMG_9220.jpeg
    172.8 KB · Views: 53
Last edited:
Just thinking , could be a silly question but could a faulty thermocouple cause a gas smell when the pilot is fired up and is running? The thermocouple is in that area I think?
No, but even if it were to be the thermocouple, you still cannot do anything.
Without being sure, you cant be making assumptions. Leave it to the engineer.
Don’t worry I’m not going to touch it . Just curious as to possible causes as I’m genuinely interested. Thought it could be the gas valve.
If cadent have come out and performed a tightness test (TT) and found a drop, it means there's something passing gas, that could be a pipe, a joint, a fitting, the gas valve train in the boiler, etc. Is there anything else in the property that uses gas?

It will be for your engineer to test and then trace and hopefully repair anything else is just guessing. It is normal to get a little gas smell (mercaptan) from the external flue when a boiler first fires up but that wouldn't show up as a pressure drop in a TT.
@Madrab thanks . No pressure drop on test but using a sensor he detected small amount of gas coming from the area at the bottom of the boiler as in the photograph. As it was coming from outside of the sealed boiler casing, he did think it was perhaps the gas valve leaking , (all of the pipes and joints were tested with spray to detect gas and were fine ) but we will see. Hopefully that makes sense?
Ah apologies, didn't get to that point properly. If it's between the gas valve and the burner then it would normal showing up as a bad joint or similar and would normally be seen with the LDF. Wouldn't be any other reason to smell gas inside the property.

As suggested it will be for your GSR engineer to trace as anything else would just be guessing.
I understand thanks @Madrab I’m assuming as the burner is actually inside the sealed casing and the gas was coming from outside the case and that’s where the valve is. Like I said, he sprayed all the joints and saw nothing but let’s see what my GSR engineer detects. I did actually know the Cadent guy because he lives nearby funnily enough and he said he couldn’t think of anything but the gas valve having checked it but hopefully the GSR engineer will sort.

Just interested because it seemed a bit of a mystery. As I say, it only occurs whilst the boiler is fired up and when it reaches temperature and is idle there is no smell. Very strange
Yes, if I remember rightly those boilers have the gas valve bellow and external to the room sealed case, therefore if gas was being detected then it would be reasonable to presume that there would be a leak on the gas train into the combustion space.

AS you say see what your GSR eng says.
What might help you change your mind about an old boiler is that your permanently burning pilot light is costing you over £100 per annum for the pleasure.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links