Gas pipe diameter - new regs

[Odyssy]

I am thinking of replacing my CH boiler, it's a Glow-worm fuel saver Mk2, 60k btu, Y plan with 9 rads. It's 15 years old and has been regularly serviced, drained, flushed and re- fernoxed every 2 years. Over the past couple of years it's been getting noisy when the heating's on - kettling initially but later sounding like a motor boat as it starts and stops.
I took the heat exchanger out and cleaned and de-scaled (chemically & mechanically) it which improved it for another year but it's getting noisy again. It's fine (mild kettling only) when only the HW is on (continuous with tank stat) but when the CH is on - rumble rumble. I've tried adjusting the pump speed and the bypass but without any real reduction of the noise.
I was considering a condensing combi to meet the new regs from next year, but I've had such conflicting information and advice about which is the best/most reliable/efficient, that I'm now going back to the idea of a normal combi which have longer track records.
From what I can glean from various websites and forums, the current gas feed pipe, 15mm copper, about 14m long with 7 elbows, will not be sufficient for the combi and should be replaced with 22 or even 28mm.
The problems in re-running the feed are such that I now think I'll just replace the existing boiler.
The question (at last) - some people say that even conventional boilers should have larger diameter feeds to meet new regs. Is this true - when the existing feed has been happliy supplying enough gas to the boiler for the past fifteen years?
Is it just another case of regulations for regulations' sake, and would the 15mm feed even work satisfactorily with say a 30ish Kw combi?
Any thoughts would be appreciated.
Thanks

 

[bripl]

the answer is NO you need a new gas supply,i would suggest 28mm pipe for the main run,you may be able to get away with 22mm but you would have to speak to a corgi reg installer for more info

 

[Odyssy]

Is that - no, you can't run the combi from it; or no, you can't run a conventional boiler from it any more.

If it's the second then it certainly seems to be 'regs for regs sake'

 

[Slogger]

22mm would that not hack it ? as 28 according to my sums is overkill i get it as 22 mm on 15 meters is ok for a 120 k btu,s has any one on here got one of them conversion cards

 

[Slogger]

corgi in its infinite wisdom has come up with another cracking idea on how to get cash from fitter and punters alike

new regs from april 2005 means a gas fitter has to inform corgi of any gas appliance they install ( where and when and how ) then corgi this is the good bit corgi for a FEE ( HAHAHA ) will send a gas certificate to the customer of the gas fitter that is already able to confirm his own work is up to scratch oh how they think these things out nice isnt it now how much will it be 70 quid for a cooker certificate on top of the install price
or is it less who knows


this is meant to cut down on cowboy installs haha thats so stupid as it will make it even more tempting to get a bodger in as the savings could be high


CORGI is a toothless mongrel with a gift for making money why cant they just (ban all sheds ) nothing personall there B.A.S from sellling gas appliances ?


WOOF WOOF

 

[leafy]

The 15mm pipe you quote is 17.5 metres long once you allow for the elbows, which will pass about 1 cubic metre of gas an hour.

That's not going to be enough for for a 60k btu boiler of any sort, so you're gonna have to fork out for a new gas run regardless.

 

[PEDANTICVINDICTIVEMAN]

If your existing boiler is working fine and getting the correct amount of gas i.e. check with manometer and or rate at gas meter with stopwatch to check, then I would fit a new boiler to the existing pipe, then check again, if still ok fine, if not then run a new gas supply, get a quote to fit new boiler without and how much extra if new run required.

 

[corgiman]

Pendant thats all well and good but he is putting combi in No way it will handle it!

 

[Odyssy]

Thanks gents, for your replies. They muddy the waters further.

bripl - the take off pipe at the meter is only 22mm dia, and as far as I remember , the yellow HDPE main that BG laid 15 years ago was about the same ID, so it would seem pointless to try to fit 28mm.

leafy - if the existing 15mm feed "will not supply enough gas for any kind of 60k btu boiler" how come the existing setup has worked flawlessly and efficiently with only the replacement of the thermocouple (twice), for 15 years? Have the laws of physics suddenly changed? (Sorry - trying to give up sarcasm)

PVM - thanks, sounds like a plan

 

[Odyssy]

Corgiman - I think PVM was referring to my plan to replace the conventional boiler rather than go with a combi. I realise that combis require a lot more gas to provide the throughput of DHW.
I think it likely that I'll forego the space benefits rather than go through the horrors of having to rerun the feed in 22mm - a real nightmare of a job.

 

[bripl]

without being able to see the job one can only make assumptions so 28mm was mentioned in case the property had other gas appliances like cooker,fire and last but not least tumble drier,it was also mentioned to seek advice from a corgi reg installer.just because the outlet on meter is only 22mm does not mean you cannot run larger dia pipes .seek the advice of a corgi reg installer

 

[PEDANTICVINDICTIVEMAN]

Yes I was reffering to swopping for existing boiler like for like, of course if a combi goes in it will have to be 22mm mininmum, having said that and not condoning the practice I have been to a property where a non reg idiot had supplied a cheap combi with 15mm which came off the meter in 15mm and ran under the upstairs floor right across the whole of the house and fed the cooker, guess what it still worked, water at bath tap wasn't red hot but was still useable, kitchen sink and wahbasin seemed fine, makes you wonder how people get away with it, the customer admitted the guy wasn't registered and only had me in to fit two radiators because the other chap wasn't too clever with the blowlamp and he didn't want the skirting burning, bloody joke, never mind the safety just dont burn my shirting board.

 

[ChrisR]

Gas pipe sizing:
First that main the other side of the regulator on the gas meter is at a much higher pressure than the pipe inthe house - so it can carry a lot more gas, and its pressure doesn't have to be held to a specific level.
(Think of high voltage cables - thin cables, less current for the same power)

The pressure regulator/governor on the gas meter tries to hold the pressure to 21mbar +/- 1mbar - though that seems to have crept to 22mbar (which helps). Transco only guarantee 14mbar!! ALL gas boilers say they need 20 mbar. Corgi say that there must be no more than 1mbar drop in the pipe between the meter and any appliance, with them all on full.
Nothing in that is a new regulation, it's always been a bit of a nonsense with the Transco guarantee.

Boilers (not all appliances though) have their own gas pressure regulators, which in the past would typically take the 20 ish mbar down to say 14 for the burner. So if the resistance of the gas pipe was a bit too much and the pressure at the input to the boiler was only 17mbar, its regulator would still give 14mbar so all is happy. Except Corgi, who would say the gas supply pipe, droping more than 1 mbar, would be "Not To Current Standard".

If the pressure available was too close to the 14mbar in the example , the regulator wouldn't cope, and the boiler would become "under gassed". To begin with all that would happen would be that the flames would get a bit smaller and the output from the boiler would go down. But if the pressure kept dropping, it would start to affect combustion in a way that could produce carbon monoxide which kills. Yes I have seen it in an extreme case. Corgi therefore decide that if a boiler is under-gassed sufficiently to affect combustion and the reason is that the supply pipe is too small, it is "Immediately Dangerous" and has to be disconnected.

Boilers are changing, particularly condensers. Instead of having say the 14mbar at the input to the burner, many boilers now have negative figures! That's because the fan in the flue SUCKS gas out of the pipe. These boilers are much more fussy about the gas input pressure. It's typical to find that if the pressure is less than say 18mbar, the boiler won't work at all.

So back to the 1mbar. Odyssy's pipe will pass about 1cubic metre per hour of gas, with a 1mbar drop across the pipe. That's enough for about 11kW (37000 Btu/hr) in theory. In practice, burrs on pipe ends, growths inside the pipe where flux was left to attack - whatever, mean you get less than the figure in the book. If you double the rate of gas being taken, you get 3 times the drop in the pipe. SO if you have 20mbar at the meter (often it's a bit less) and lose 3mbar in the pipe, you don't have enough pressure to even light some boilers.

For the length of pipe in the example, 22mm pipe with a 28kW combi boiler would be marginal. So it has to be 28mm.

 

[Odyssy]

Aha - the mud is beginning to clear.

Thanks ChrisR - excellent answer that explains a lot.

PVM - your plan of fitting a new conventional boiler and see if it's OK and if not rerun the feed in a larger size kind of shoots itself in the foot - if I have to do that then I may as well fit a combi in the first place.
I suspect that I will have to bite the bullet and put in a 28mm feed. The only other appliance we have is a rarely used coal effect fire (although Mrs Odyssy is lobbying for a dual fuel range cooker during curent kitchen rebuild).

Anyone got a large Corgi registered ferret that would be willing to help solve major 'access to pipe run' problems?

I suppose the only other option is a new heat exchanger for the existing Glow-worm, but I've been told 'you can order one but it might be months - glow worm wait till they have orders for several before making any'.

Is this b*****ks or does anyone have them on the shelf?

That of course would possibly show up age related weaknesses elswhere in the boiler - what other components 'go' or become less efficient?

Thanks for your help.

 

[ChrisR]

Gas pipes get to strange places! Apart from on the wall outside, they can go behind large covings round the ceiling, or under kitchen units.

It's quite common to have only the built-in oven removable, so you have to cut a lot of 2ft long bits of 28mm and solder a bit on, slide it along, solder another bit on... etc, until you come to a hole in the wall you drilled from under the stairs..