Gas Hob issue

[Alfie25]

I know this isn't central heating but I thought the gas pros would read it so I'm posting here.

I've got a gas hob and when the weather is hot the gas supply to it exhibits some strange characteristics. In hot weather, when you turn the gas knob for any of the rings to ON, and light it, the gas surges through quite forcefully, you can hear it more than normal, then within a couple of seconds the supply almost dries up and the flame almost goes out, then a few seconds later the supply stabilises and the gas comes through normally.

This only really happens in hotter than average weather, like today for example. Any ideas to what could be the cause?

 

[gasmanstu72]

sounds an odd one to me,
do you have any other gas appliances?

 

[Alfie25]

Yeah a combi gas boiler which doesn't seem to be affected by this problem, possibly as when it fires up its taking more gas through from start up. I guess the hob takes less gas through so the surge then drop then stabilise cycle is more noticeable.

Could the supply or governor on the meter be to blame? The gas box is on an external wall and gets plenty sunshine on it.

 

[gasmanstu72]

natural gas does expand when it gets hot, but not massively,
the governor at the meter should provide you with a constant pressure, is it an old governor? its difficult to tell if you're not seeing them regulary, but some older ones can cause problems, especially Donkin ones.

it could be worth calling out transco to have them test your pressure

 

[picasso]

If your gas pipes are in the sun the gas pressure can rise enough to give the symptoms you have described.

 

[Alfie25]

natural gas does expand when it gets hot, but not massively,
the governor at the meter should provide you with a constant pressure, is it an old governor? its difficult to tell if you're not seeing them regulary, but some older ones can cause problems, especially Donkin ones.

it could be worth calling out transco to have them test your pressure

The governor was newly fitted about 2 and a half years ago shortly after I moved in, as there was a slight gas leak on the old one. The pressure and supply is OK for the gas hob and my 30kW combi. The problem is this build up of pressure on warm days. It's like the governor is stuck and lets through gas a fast rate, then throttles down the supply too much to overcompensate (at which point the gas hob almost extinguishes) and then stabilises to the normal rate. On one occasion the supply dropped enough to cut the flame out for a split second so when it came back on I had unlit gas coming straight through. This is my main concern.

I'm keen to call out Northern Gas Networks but these characteristics only happen after a period of sunshine/warm weather so I can imagine it would be tricky for them to diagnose. I suppose there's a chance the replacement governor was duff and if they replaced it again it could rule it in or out as the culprit. If my current one was duff, would I have more problems?

If your gas pipes are in the sun the gas pressure can rise enough to give the symptoms you have described.

The 2 foot or so of the pipe from the ground directly up to the meter box is in the sun, as is the whole meter box itself, so not as if I have huge run of external gas pipework.

 

[gasmanstu72]

The 2 foot or so of the pipe from the ground directly up to the meter box is in the sun, as is the whole meter box itself, so not as if I have huge run of external gas pipework.

this is the service pipe that is before the governor and its at a higher pressure,
the governor then regulates the pressure at the outlet, so if its in the sun shouldn't make any difference, if your outlet pipe is in constant sun it might increase the pressure giving you that surge you're talking about.

give Transco a call, it won't cost you anything and they will test the pressure.

you could also have a blockage in your pipework that will cause similar symptoms.

 

[Alfie25]

this is the service pipe that is before the governor and its at a higher pressure,
the governor then regulates the pressure at the outlet, so if its in the sun shouldn't make any difference, if your outlet pipe is in constant sun it might increase the pressure giving you that surge you're talking about.

give Transco a call, it won't cost you anything and they will test the pressure.

you could also have a blockage in your pipework that will cause similar symptoms.

In that case the service pipe/inlet is in the sun (like most homes) but not constant sun as it faces west so it's afternoon only. The outlet pipe goes straight from the meter and through the cavity wall, so it's a normal set up. The meter box gets hot and the heat could radiate into the outlet pipe I suppose but I can't see how that's different to most homes.

Just read this too, so I think a phone call is in order:

http://www.northerngasnetworks.co.uk/gas-emergencies/got-low-gas-pressure/

 

[Agile]

I would say that your "problem" is due to the gas in the meter expanding and giving an initial burn at higher pressure.

You will find its longer on the small burners compared with the large ones.

Starting the boiler for a moment before lighting the hob will remove the problem.

My advice is to ignore it as its irrelevant.

Tony

 

[Alfie25]

Thanks Tony, I would also see it as irrelevant were it not for the fact that the flame has once extinguished completely, leaving unlit gas to come through. I've been reading about thermocouples/flame failure devices but my gas hob doesn't have this feature.

I can understand the initial burn at a higher pressure, but why after that doesn't the flame subside to a normal level? Why should it get to the point of almost extinguishing - i.e. no gas coming through?

I suspect it may well be just 'one of those things', albeit an unusual thing. Have you come across it?I live in the north so it doesn't get that hot up here! I suppose there'd be no harm in getting Northern Gas Networks out to check the meter box.

 

[Agile]

I am only, to an extent, guessing at your problem.

But I think I am correct at the cause.

But the gas pressure regulator can be somewhat "sticky" to unlock when the pressure on the outlet side is high. They lock up if the pressure on the outlet becomes too high.

If you call them out they could change the regulator ( called "governor" in gas speak ) and a different/new one should not exhibit the dip in pressure.

Tony

 

[Alfie25]

Thanks again Tony. I had a new regulator fitted in 2012 - are these adjustable at all or can the spring be lubricated?

And when you say 'outlet side' you mean the meter and beyond into the house? I suppose the heat generated inside the box will heat up the meter and increase the pressure after a few hours direct sunlight.

 

[muggles]

They're only mantainable by the gas transporter, it's definitely not DIY (even us mere Gas Safe Registered Engineers aren't allowed to touch them). As an experiment, try blocking the sunlight from getting to your meter box to see if it improves the situation

 

[Agile]

The old ones were totally able to be taken apart.

Now they are all sealed and just replaced. Although the output pressure can be adjusted under a sealed access.

The older gas meters have a considerable volume and the inside of the meter box can get up to significantly over the ambient air temperature thus heating up the gas in the meter.

Tony

 

[gas112]

So pray explain to me agile why half the country is not having this problem .
And what are all sealed and just replaced are you on about meter regs if so your talking even more sh#te.

OP just call out the emergency service provider for your area to get it checked its free and they will be out in a couple of hours