Gas pipe not big enough

29 Dec 2010
Reaction score
United Kingdom
Hi , im after abit of help , i am currently looking around for a combi boilers to replace our old back boiler set up ,
i live in a three bed hse with 7 radiators , which at the minute are being fed from the old manifold under the floor boards via 10mm pipe .
I have a couple of issues im struggling to decide , My first one is
would it be possible to leave the old manifold in and run the combi to it , to feed the rads or do i just rip it out the manifold and run 22mm to each rad and branch down to 15mm ?
Im also struggling to decide which combio to go for . Im planning on fitting a mixer style shower so ideally i need it to be able to supply a good hot water pressure . ive seen the greenstar 37cdi from bosch which is capable of supplying 15l/min , our incoming cold water pressure is more than adequate to maintain this 15l.min so happy on that front its just the gas size im abit stuck with , which is turning out to be a nightmare . Ive checked our gas supply and it appears to be only 3/4 track pipe and on the fitting coming out of the track pipe it says 20mm ...Now im no expert on pipe sizing but doesnt any modern half descent boiler need at least 22mm ? so it apears im well screwed .
Can anyone help me in what to do next . do i go for a smaller boiler or is it possibly for the gas board to come and put abigger track pipe in and increase the pipe upto the meter . which is also only 6m3/hr meter the pipe coming out of the floor looks to be adequate ....

Helllllp...... :mrgreen: :(
Sponsored Links
If the flexible pipe you refer to is on the inlet of your gas meter (anaconda) it is upstream of the meter governor and as such is at a higher pressure, therefore can pass a much higher gas flow, you only need to concearn yourself with gas pipework downstream from the meter, a U6 meter will pass 6m/3 per hour which equates to a little over 60Kw/h so unless you have a lot of other large gas appliances in your house means that your meter and incoming main will be more than adequate

you should be able to run a pair of 22mm heating mains to your existing manifolds without problem just make sure you power flush the system if your new boiler's warrenty calls for it! ;)
Thanks for your help boilerman , i apreciate it .....Ive been doing abit of research regarding connecting a manifold that has 8mm microbore pipework feeding upto 7 rads onto a new combi boiler circuit and that problem of powerflushing to avoid the warranty being void keeps popping up .
Whats the going rate for having a system with 8mm pipewrk flushed ? and what does it ionvolve exactly . Is it a sort of flush through with some form of pressure washer . I bet its a bugger to do ,
If after having the system flushed would this system work efficiently and well, connected to such a high spec boiler such as the 37cdi greenstar bosch ? and do you know if manufactures instructions supplied by this boiler model say using a manifold and microbore would be ok ....
Im sorry about all the questions but my heads fryed with it all .lol....I dont know alot about boilers as you may well tell :eek: , Im only a commercial laundry and catering engineer...
Ive been trying to source a brass union/fitting to fit onto the out going side of my gas meter to try and make the outgoing side 28mm , Does anyone have any ideas were i could get one from or even the 22mm size if they do a 22mm theres a good chance they might help me further , as the lad behind the plumb centre didnt even know what a u6 gas meter was ... :D , I havent had chance to get to crosslings yet . Will they do them ? cheers
Sponsored Links
I dont think the GAS guys on this site will be too happy you altering your own gas pipes.
Probably something to do with having to be competent working with gas to do it - I.e a registered gas installer
I am competent . and also a registered gas installer ( not that holding gas tickets makes you competent ! )
ive come across some right plonkers holding tickets in my 14 years of working on gas , so in my opinion holding a card to say your gas safe registered does not make you competent.
There is some good assesment centres and some totally incompetent ones .
I had a plumber who works for the local council trying to tell me if i wanted 28mm coming out of my meter i should buy a 22mm fitting and step it up ....HAHAH . .
I was commisioning in a new build nursing home last year and whilst i was commisioning the catering equiptment I found when on a working test the pressure dropped from 21mb to 10mb , on further investigation i found the pipe feeding a big fryer , range , and a grille was 22mm , I then worked out the pipework needed to be 42mm copper to the kitchen alone . on investigating the meter i also found they had stepped up the pipewrok coming out of the meter as the pipe coming out of the meter was significantly undersized , This was installed by a big company who are gas safe registered . I thought that was rather incompetent me self
Ive never had much experience working on gas meters so unsure of the sizes and options available to me in making my outlet of my gas meter 28mm . Ive worked the gas requirments out and 22 is borderline for the piping route i had in mind for my fire and cooker tops as well as me boiler , I dont really want to start chasing out the floor to reduce lengths and flow rates , so i think im doing the right thing in doing it properly , I dont want to call a bosch engineer out to tell me the pipe is undersized after running it all in 22mm with tees to me fire and cooker

So all i am after is abit of friendly advise not a lecture on me being competent or not ....Thanks
Can anybody help me
Funny, I thought your first post said

..Now im no expert on pipe sizing but doesnt any modern half descent boiler need at least 22mm ? so it apears im well screwed .

Now in your last post your suddenly an expert in it.........
If you have a gas ticket then register for the CC and you can ask your questions there.......although as has already been said i am suprised you need this sort of advice.......if you already have a ticket that is
Thats correct i am no expert on pipe sizing i never for one minute said i was did i ?? ?? ,
But i can do it its not bloody rocket science is it ?
Your correct i asked if any half descent boiler requires 22mm gas feed , and i was screwed . as mine is 22mm coming out of the top of the meter ,
Whats odd about that ?
Seems you are just a smart aSS TO ME especially with a name like you have ...... , if you have no worthwhile advise for ime i sugest you keep your bloody neb out and your feeble opinions to your self . ! ! ! ! !
Ive never installed a boiler but was under the impression a big kw rated one would require at least a 22mm feed , so to tap off a 22mm pipe to a fire and a cooker and have rather long runs is not a good thing and I never even sat down and worked it out i just used my rough charts in my books i got when i went on my gas courses , I know they are slightly overrated but bigger is better than smaller .
Im sory if i come across nasty im not like this , its just all im after is abit of advise and i get idiots who pretend they are smart preaching to me and trying to make me look a fool .
Sory powel that post was not meant for you mate . cc forum ?
Ive never installed a boiler and never had to change a meter mate .
Do you know then were i could source a fitting and is it possible to do ?
As Powell30 suggests, join the CC and you'll get all the advise you need. As an RGI you'll appreciate that DIY info on working with gas is not something that should be given on a general forum!
Thanks mark i do appreciate that , im new to these forums and genuinly thought it was a forum for installers and the likes as ive read quite a few posts on installing boilers and things concerned with gas so assumed it was ok to speak on open forum about these matters .
Im unsure of the cc tho , could you enlighten me please...Thanks alot
Apologise to anyone i may of upset with my post I just carnt stand smart AArs es thats all .....
The CC is the Combustion Chamber, email admin with your Gas Safe number and they'll let you in, you can discuss gas work there

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