22mm to combi boilers? 15mm no good?

[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