Not enough gas

[Pete Verdon]

I have an all-gas cooker with six hobs and one large oven. However, it can't cope with having all of these on at once - even three hobs sees the flames on each reduced dramatically from their one-at-a-time sizes. I guess this could be a restriction either inside the cooker itself, or in the supply. In the former case, no problem, as I've just forked out for a new cooker to be delivered in ten days or so (the current one is a bit crap). However, there is the possbility that the fault is in the house piping, or a deficiency in the actual supply.

The pipe is hidden behind the cooker, which I don't really want to pull out just yet. However, I can see into the space from one side, and it looks like there are two sizes of pipe in there. It emerges at a larger diameter (maybe 3/4") but for the last foot or so before the connection to the cooker, it's reduced to a smaller size more like radiator pipes (sorry about the vagueness of the sizes, but it's a little while since I last squinted through that gap. I guess there aren't that many sizes of gas pipe in use anyway.) Is this normal? Likely to be a problem? I would have thought that the tubing inside a cooker is pretty small anyway.

Any advice welcome.

Pete

[Lobster]

From the info given I'd say the most likely culprit is the piping in your house. It sounds like it's done mostly in 15mm tubining (that's the next size down from the 22mm or 3/4" which you can see). What happens at the gas meter end of the tube, by the way - presumably you can see the tube diameter there?

Although there will be very small tubing withing the oven, yes - it's all about the overall length of the narrow tubing which the gas flows through as that's what determines the resistance to the flow. If there's only a very short distance between the incoming pipe at the gas meter and your oven - and there's nothing else fed with gas eg a boiler or fire - you'd probably get away with a 15mm pipe.

I've seen a rule-of-thumb pipe size calculator posted here before but can't find it - hopefully someone else will know?

David

[Tim Downie]

?? From what the OP's said, it sounds like 22mm up to the last foot when it's reduced to 15mm. Seems unlikely then that the system from the meter goes from 22mm to 15mm and back to 22mm before reducing to 15mm at the very end.

Tim

[TheScullster]

"Tim Downie" wrote

Would be useful to know: The pipe route/length and number of elbows from the meter Was there another heavy user on line when the tests were carried out? Have there been performance issues with other users eg boiler?

Phil

[Lobster]

Yep - true enough. Sorry, misread the OP!

David

[Pete Verdon]

Don't know, unfortunately. As the crow flies it's maybe 20, 25 feet, but I have no idea of the route. I suspect it's buried in the concrete floor, but there has been an extension between the meter and the cooker (though those are both in original parts of the house) so anything could have happened.

The only other gas appliances are a living room fire (which I never use) and a smallish combi-boiler. I haven't noticed any issues with the boiler.

I haven't specifically tested the cooker with the boiler off, but it's likely that it would have been off at least some of the times that I've used the cooker, and I haven't noticed any significant variation. Interesting idea though - I guess if I turn the cooker on when the boiler is on, then go and turn the boiler off, I could compare the flame size on the cooker. If it doesn't change, then that suggests that the incoming supply is unlikely to be the bottleneck.

Pete

[dave]

have you had a new gas pipe to the meter as done by transco? our area has and all they do is line the old pipes with new plastic making it a smaller supply line to the house.

Dave

[Pete Verdon]

Not while I've had the house, but that's only six months. However, the house is 1990s, so I wouldn't have thought the pipes would have needed replacing yet.

Pete

[cj]

Hi Had a similar problem 2yrs ago with a range cooker ended up having to repipe in 28mm to solve problem. IIR gas needs volume not pressure to work so the piping change restricts the flow. Most instalations leave the meter in either 28 or 22mm copper then reduce to

15mm for the cooker outlet but continue in 22mm to the CH boiler if it further away.

HTH

CJ

[Ed Sirett]

What's happening at the outlet of the gas meter? with a bit of luck the governor's shot and the whole problem is NG Transco's.

[Pete Verdon]

Sounds ominous. The new cooker, though a range type, has electric ovens and grill (I hated the gas ones in the old cooker - seemed so primitive). Hopefully no major replumbing will be necessary to get five rings working properly.

Treading on slightly sensitive ground, is cutting off the 15mm extension and fitting a (presumably bayonet) connector to the 22mm something that's DIYable? If this were water I'd be at it without a second thought, but are there any special considerations for gas? What type of fittings are used (solder, compression, etc)? I realise there's an argument that says that if I have to ask such questions I shouldn't be doing it, but one has to start somewhere.

Pete

[Tim Downie]

I would have thought that if it's only 5 rings *no* replumbing should be necessary. Surely it must have worked properly when installed (although I appreciate that you don't know this)?

Makes me think that the pressure regulator by your meter isn't doing its job properly.

Tim

[Pete Verdon]

I didn't see anything of note when I read the meter the other day. What should I be looking for?

Pete

[Tim Downie]

You won't see anything at all on the meter. It's the pressure that seems to be lacking in your pipework and that'll have to be tested with a suitable gauge.

From what you've said it's clear that not enough gas is getting to your 5 ring hob. Also, from your desription of the pipework, that doesn't sound like it the source of the problem either.

That leaves either a problem with your hob (possible sticking shut off valve if it has a closing lid) or a lack of supply pressure. If your cooker has a lid I'd try working it open & closed a few times to see if that frees anything up. If it doesn't have a shut off valve, I'd suspect that your pressure regulator by the meter is faulty which, as Ed says, is Transco's problem to sort out.

Tim

[Pete Verdon]

Thanks - a useful summary. There's no lid valve on the cooker as it's a range type appliance. It's being replaced anyway. I reckon the thing to do is take a manometer reading while I'm disconnecting it, hoping that that's good and it's the cooker that's faulty. If it's not, I can connect up the new cooker anyway, and then call Transco to sort out the regulator.

Pete

[Ed Sirett]

Read the gas fitting faq. There's more to gas meters than the reading 8-)

[Ed Sirett]

If the boiler is working OK, and specifically if the boiler coming on does not noticeably affect the hob flames the the problem is with the range-cooker. One possibility is that the bayonet connector is only half in, enough to seal but not enough to latch and more importantly depress the button inside the connector. As a result you not got a good enough gas supply to the range cooker.

You really need to attach a manometer (around £20 or make yourself if you have /lot/ more time than money) to the gas meter outlet test point. Then record the pressure as you go from 1 to 6 rings alight and/or boiler You should find that the pressure will drop a bit but should stay in the range 19-23 mbar whatever the flow rate.

[Tim Downie]

Ah, I hadn't thought of that one. Good one to remember.

Tim

[cj]

Hi agree with later repies 5 rings should be fine on 15mm my cooker had 8 plus

2 ovens so really ate the gas.

You say house is 90's? so lead gas piping is out. As sugested suspect regulator or (if the meter is under the stairs or obstructed) check the gas valve is fully on.(I know this seems basic but had a case when kids pushed cases under stairs catching gas valve turning it off) Or look for damage to the piping ,has it been crushed?

As has been said the easiest way is to use a manometer at the cooker . As for your other question gas fitters solder connections and also use compression fittings.Normally compression is only used where accessable but have heard of a pushfit used on propane (don't know if its legal or safe though) HTH

CJ