22mm to combi boilers? 15mm no good?

[kirkgas]

The pipe size depends on the Kw of the boiler, how far away the meter is, how many bends, other appliances on the same pipe. If the gas pipe inlet on the boiler is 22mm then 22mm pipe is required all the way.
If the boiler is running on 15mm pipe. Check the inlet pressure on the boiler when the boiler is working full bore and any other appliances on the same pipe are running.
The pressure should not drop more than 1mbar than the same test taken at the meter
Low inlet pressure can lead to incomplete combustion, a rise in carbon monoxide and any warranty from the boiler co. being void!
Best practice is to allow for the pipe size upgrade in your Quote

everything you have said is correct but i would add there is a distinct possibility of gas starvation to another appliance if you run a combi on 15mm pipe, eg cooker (which doesnt have FSD) is on and working, someone opens hot tap and combi fires up on full gas, depending on layout the cooker gets starved of gas and goes out, tap is shut boiler goes off and supply is reinstated to cooker which now has 3-4 rings passing full rate gas with no ignition

 

[td1947]

Well newbei1, I did not mention a backhander, OR £50. Are you saying that when GS engineers are asked for Landlord Safety certificates, the requestin LANDLORD ALWAYS knows the appliances have been professionally installed?? A landlord could have just bought several properties, and would not have personal, or even easily verifyable knowledge, about who installed what. I was talking about the GS CERT offered for about £40, on a legitimate basis. Is it not the duty or right, of any GS registered person, to report, via the GIUSP rules, the ID, AR, or NCS state of an installation?? I would have thought than these inspections potentially create MORE business, if a DIY'er does it badly. I beleive that some keen DIY'ers do the main install/plumbing grunt-work, but leave the actual gas connection and commissioning/testing to the proper GS registered person (a sensible thing to do I would have thought). In these economic times, would this sort of work be refused then?

 

[newbie1]

in a word yes
i am sick and tired of people who think its ok to do the work and then expect a gas engineer to pop in and sign the work off
i would not sign off any work i havent completed
doing a landlords cert and signing of an install are 2 completely different things
let me guess just a wild stab in the dark td1947 you are not a gas safe registered engineer
and if a diyer does it badly people can die and as such i dont want any tom dick or hary doing a bit of diy gas work no

 

[heatserve]

Halstead Eden *snigger*

 

[spudulike]

I'm looking for some advice and help - I have just had a combi boiler installed by a Gassafe registered fitter. All neat and tidy and it looks a good job.

But - the boiler is connected to the old 15mm pipe from the meter and is then taken up to 22mm for the last few inches at the boiler. Even though there was lots of discussion before starting the job about how to get under the floor and replace the pipes not a single floorboard was lifted. He is telling me that the pressure at the boiler is sufficient (although I do not think he has tested it with gas cooker and fire on at the same time.)

The boiler is about 5 metres from the meter in a straight line but the pipe is under the floor so probably has a few turns.

I am now worried that the boiler will underperform, be uneconomical and possible unsafe ?

Is the wider pipe a legal requirement ? Or if he proves that there is still adequate pressure even when all other appliances are running is the narrow pipe still okay ?

All advice appreciated.

 

[kirkgas]

safety is paramount, the MI's take the appliance requirments as paramount and might ask for 22mm pipe, if so easy peasy he is wrong, if the MI ask for a specific pressure then a test according to the gas regs and BS6891 needs to be carried out to determine what is required, if the pipe is wrong thew boiler under performing is the least of your worries more likely to create a prob at the fire or cooker, post the make and model of the boiler and also a distance/route as best you can for the 3 appliances

 

[Billy Bob Bob]

everything you have said is correct but i would add there is a distinct possibility of gas starvation to another appliance if you run a combi on 15mm pipe, eg cooker (which doesnt have FSD) is on and working, someone opens hot tap and combi fires up on full gas, depending on layout the cooker gets starved of gas and goes out, tap is shut boiler goes off and supply is reinstated to cooker which now has 3-4 rings passing full rate gas with no ignition

and this is exactly why we have pipe sizing,because this situation can and does happen

 

[spudulike]

safety is paramount, the MI's take the appliance requirments as paramount and might ask for 22mm pipe, if so easy peasy he is wrong, if the MI ask for a specific pressure then a test according to the gas regs and BS6891 needs to be carried out to determine what is required, if the pipe is wrong thew boiler under performing is the least of your worries more likely to create a prob at the fire or cooker, post the make and model of the boiler and also a distance/route as best you can for the 3 appliances

The boiler is a Worcester Bosch Greenstar 30Cdi combi. Distance from meter I guess at 5 metres. Gas hob is probably 3.5 metres. Gas fire is about 5 metres. These are straight line distances and as the pipes are all under the floor I don't know whether they have any turns.

The fitter is coming back to the house early next week - what should I be asking him to test or prove ? If he still insists this is a proper install can I get it checked independently somehow ?

Thanks for the advice - much appreciated.

 

[tamz]

A 30CDi requires 3.4 cubic metres of gas per hour to operate correctly. A 6m length of 15mm pipe (which is what you will have when adding in fittings) can only pass 1.9 cubic meters of gas so your boiler is working at just over half capacity at around 18kw.
The situation is made even worse as you have a fire and cooker and could lead to a situation as Kirk said where the other appliances are starved of gas.
Get him to do a gas rate of the boiler whereby you turn the boiler on to high rate (hold the chimney sweep button for about 10 secs) and time it at the meter.
Eg. A rough (but near enough) guide is
Metric meter (m3) time it for 2 minutes then multiply by 321 = kw
Imperial (ft3) 1092 divided by the time for 1 revolution of needle = kw.
You will need a 22mm pipe from meter to the boiler (22mm is stated in the manufactures instructions).

 

[fuzzy]

work out the gas requirement then you know!

wouldnt someone who had done their acs know this?

 

[spudulike]

A 30CDi requires 3.4 cubic metres of gas per hour to operate correctly. A 6m length of 15mm pipe (which is what you will have when adding in fittings) can only pass 1.9 cubic meters of gas so your boiler is working at just over half capacity at around 18kw.
The situation is made even worse as you have a fire and cooker and could lead to a situation as Kirk said where the other appliances are starved of gas.
Get him to do a gas rate of the boiler whereby you turn the boiler on to high rate (hold the chimney sweep button for about 10 secs) and time it at the meter.
Eg. A rough (but near enough) guide is
Metric meter (m3) time it for 2 minutes then multiply by 321 = kw
Imperial (ft3) 1092 divided by the time for 1 revolution of needle = kw.
You will need a 22mm pipe from meter to the boiler (22mm is stated in the manufactures instructions).

Tamz - Thanks for this and to other posters' replies. I'm now convinced he needs to upgrade the pipe. Are there any pipe sizing regulations I can quote to block any objections he might have ? Sure I've seen these in a previous thread but can't remember where.

The other thing I was thinking of doing, if he refuses to change the pipe, was to get an independent inspection done. Any ideas on how to do this ?

Thanks again

 

[oldplumber]

contact the gas safe register, let them know you are unhappy and having sought advice request them to carry out an inspection for you. If your really worried call in another fitter, checks his/her credentials so you know they are qualified and ask them to survey your sytem, youll have to pay them but youll get a simple report which if things are wrong you can refer to gas safe and trading standards and use to claim you money back from the original fitter if he fails to make good the work, which you must allow him to do if your to have a valid case if things dont work out in the end. have fun!

 

[spudulike]

Good advice - I'll give the fitter a chance to put it right first and then if no joy I'll call gassafe and see what they say. There is also a local plumber who I know is reputable and I'll get him to do a check.

At least I haven't paid yet .....

Thanks

 

[kirkgas]

Tamz - Thanks for this and to other posters' replies. I'm now convinced he needs to upgrade the pipe. Are there any pipe sizing regulations I can quote to block any objections he might have ? Sure I've seen these in a previous thread but can't remember where.

The other thing I was thinking of doing, if he refuses to change the pipe, was to get an independent inspection done. Any ideas on how to do this ?

Thanks again

BS6891 covers gas pipe supply requirements

 

[Eddie Charlton]

it should purley be down to what you calculate, taking the total kw usage at the address and the pipework layout to get from the meter to each appliance. dont take it for granted that the exisiting pipework was correct in the first place. the new boile might say that it will be acceptable to connect to 15mm, but that is only half the story. get someone in to survey the address to calculate the correct size pipe needed. it does not take long

 

[Bernie2]

All this confusion seems to back up a good reason why there should be a website with freely accessible gas work information for everybody.

We could then standardised the info and all work out of the same info.

The problem is the gas Regs are so uninformative and leave it open to interpretation as the forum shows. Some are quoting from manufacturers specs, some from British Standards and some from ACS or training courses. Its all a mess.

The likes of the Building Regs guides are straight forward and easy to get for free.

Why not do the same thing for gas work?

 

[Hoopey]

Have a look in the Manufacturers Instruction, newer worcesters and vailliants can work at 17mb inlet pressure there that economical. Tricky one though.

 

[tamz]

It has nothing to do with being economical. Most boilers will actually work ok at 17.
The point is that BS6891 states
"The pressure drop between the outlet of the meter and the points to be connected shall not exceed 1 mbar at maximum flow conditions"

 

[Assessor Gas]

Hi Tamz, I am a field assessor and inspector. Simply you need someone who knows what they are doing. It doesn't take 5 mins to size up pipework which is necessary on the majority of new installations these days due to the higher overall demand. Most people are missing the downside, and since i have inspected a lot of downsides, an undergassed boiler scales the Heat Exchange fins due to condensing in the combustion area. When the heat exchange blocks slowly you get vitiation and excess heat in there and then you get 2 problems. Incomplete combustion, and excess heat in the combustion area to burn through your seals. When checking G20 operating pressures you must run all the appliances not just one. Now check your pressure losses, and perhaps gas rate with all appliances on. From a safety point of view - well i thought that's what gas engineers training was for, and why the job prices are high. The customer's interests need to be in hand. For 10 years i have had to listen to "22 it will do" - Monkeys - If you got 15 in there even worse. funny enough just come from ispecting one today. Call Gas Safe, They want to hear from you !!!!! Good Luck