Is there such a thing as "Dirty Gas" and could it damage my combi?

[Nick Odell]

Cooking on the gas hob last night, suddenly the flames began to flicker yellow.

First thought: dirt on the bottom of the pans - so I turned on the other burners and they were doing the same.

Second thought: low oxygen (panic!) but even though I felt no personal effects and the house is old and draughty as hell, I opened the back door and continued cooking with the open air blowing into the kitchen. It carried on like that for another few minutes and then it went away leaving only normal, blue flames.

Everything is AOK normal this morning and it's never happened before so is it reasonable to presume there was some contaminant in the pipe? If so, could it have damaged my combi? Next combi service is due in about nine months.

Nick

[Andrew Mawson]

Low gas pressure would do that.

Possibly a short term massive leak on the local supply down the street - anyone working down a hole in the road nearby?

Andrew

[Nick Odell]

I'll have a wander round later and take a look.

Thanks,

Nick

[newshound]

Alternatively a little bit of salty water in the system? There's "incomplete combustion" yellow (daffodil?), and Sodium yellow (a bit darker and closer to orange, like old fashioned low pressure sodium lights). Actually you don't need salty water, there will very likely be dried salt in the burners, just a few droplets of water to mobilise it?

[Brian Gaff]

Well, it could have been foreign bodies but apparently they burned offwith no problems so one would assume the same is true in a boiler. It would be pretty naff boiler if it could not cope with some pollution to the gas. I don't expect you will ever know what it was, another form of gas, some water, who knows? Brian

[Nick Odell]

Could be: I had just poured the pasta into the boiling salty water. But it's not something I've noticed before and, for the avoidance of doubt, I have boiled pasta in salty water on that stove before :)

It didn't do it again. Still, it gave me an excuse to clean all the parts, dry them and put them back together and it is still working just as it always has. Just one of those things, eh?

Thanks,

Nick

[NY]

When a pan of salty water boiled over, it affected all the burners of the hob and also the gas fire in the next room (and maybe the boiler - can't see the flame). I wonder if some water managed to flow backwards down the pipe beyond the hob to a common feed for hob, gas fire and boiler. It took a couple of weeks to go away, even though I cleaned all the burners as soon as it happened.

It only take minuscule amounts of salt to tint the flame: I remember from chemistry that the flame test is very sensitive.

I've noticed that fir cones dipped in copper sulphate (sold to brighten up an open fire or wood-burning stove) cause *all* the flames to go blue, not just the flames from the cones themselves.

[Harry Bloomfield]

Nick Odell laid this down on his screen :

Sometimes water or moisture gets into the pipes from them working on them. Sometimes so much gets in it can cause problems and they have to drain the pipes down.

[The Scottish idiot ...]

the west coast of scotland gets iron filings through the supply but the east coast doesn't ......work that one out.....

[Harry Bloomfield]

NY explained on 09/01/2019 :

Very unlikely that water could manage to makes its way back through a tiny gas jet, a jet which would be preceded by the air mix holes.

[newshound]

Surely the jet is before the air mix holes? In any case, many jets have a large diameter counterbore on the upstream side before the actual metering jet.

[Harry Bloomfield]

Not so far as any spilled water is concerned. Water would spill out of the air inlets, before it could get to the jets, then into the pipe work.

[newshound]

But if you follow the thread you will see that *I* wasn't talking about spilled water in the gas. Spilled cooking water can deposit salt on the burners. Water *in the gas* can spray out of the jets as an aerosol, pick up dried salt on the inside of the burners, and carry it into the flame.

[ss]

Thats due to the electric brae :-)

[harry]

Probably something you've spilt on the burner evaporating and burning off.