15mm gas inlet pipe, how big a problem?

[poppins]

From a discussion over a new combi boiler :

With any significant length of 15mm pipe between boiler & meter, there will be insufficient gas to power the boiler.

Not quite sure which of the boilers being discussed croydoncorgi was referring to here, but we are having a Worcestor Greenstar 25Si installed on a 15mm gas inlet pipe that seems to go as far back as the cooker (3 metres of pipe), and probably all the way to the meter (about 10 metres).

Is this going to be a disaster? Will the difference just cause the boiler to underperform, or will it lead to it breaking down sooner? Or will it not be a problem?

Replacing the pipes would be a major piece of work.

Any advice would be much appreciated. Ta.

EDIT: Corrected model number

 

[bogstandard]

Impossible to say. Obviously it would be preferable to have the pipe to the gas cooker in 22mm (3/4") pipe and from there in 15mm. One would have to monitor the position with the cooker on full and likewise the Boiler

 

[Bahco]

Your corgi will probably insist on upgrading the pipe to 22 mm. Man Instructions will probably specify 22 mm piping. RTFM

 

[ChrisR]

Disaster would just about cover it. I expect if you do the sums properly it'll come out to 28mm, most of the way.

You need something like 3 cu m per hour
Look here:
http://www.cda.org.uk/megab2/build/pub124/sec3.htm#4.3 Copper Tube Sizing

Then go on the cautious side because the tables are miles out.

 

[kevplumb]

a three m straight lengh of 15 mm pipe will dishcharge 2,9 cu m an hour

the boiler requires 2.98 without the cooker on

so it is undersized as i cant belive there is not a bend or elbow on it somewhere IMHO

and if it is in 15 all the way to the meter and it is straight it will disscharge 1.1 cu m per hour

your boiler will be woefully undergassed

 

[poppins]

Your corgi will probably insist on upgrading the pipe to 22 mm. Man Instructions will probably specify 22 mm piping. RTFM

I did RTFM, and it specified that the intake was 22mm, but didn't clearly state what it needed the actual piping in the system to be (rather than just what it was at the point of connection). The Bosch Worcester site did give calculations for the gas flow for different pipe combinations, but it didn't even cover 15mm except with LPG, and I didn't spot gas flow requirements (though I was just sneaking peeks at the documentation whenever my boss wasn't looking!)

This thread is worrying me! Should I be able to ask the plumber to test the discharge rate at the end of the pipe, is this something that can be easily done?

Would it be wise to replace the pipes after the installation? Or will it in anyway damage the boiler to be undergassed?

The pipes run from front to back of the house through concrete flooring, replacing them would be a complete and utter nightmare, and would probably take longer (including time to save up the money) than we'd be happy to wait for heating and hot water (especially with this well timed extra cold snap in London!).

Thanks again for all your advice

 

[poppins]

Ok,

Now I've had a bit more time to read the manual and have found the following ...

It is important that a gas supply pipe of at least 22mm
diameter is used. Under no circumstances should the size of the gas
supply pipe be less than that of the appliance inlet connection.

uh-oh.

Or is it just making the obvious point that the pipes should fit at the point of connection (and not just plug the gaps with selotape!)

 

[ollski]

If you are having to do pipe sizing for your installer I would advise finding a new installer.

 

[poppins]

If you are having to do pipe sizing for your installer I would advise finding a new installer.

It was the installer who pointed it out. But both he and another installer (both CORGI registered, both recommended by the manufacturer's website) said that for the 24i, the pipesize would not be an issue (I assumed that you could just use an adapter and that for a small enough boiler the gas flow woud be sufficient).

Are they just talking nonsense?

As you can probably guess I know very little about plumbing ... ask me a question on post production information technology and I'll begin to sound a little less stupid

Thanks again.

 

[ChrisR]

Verily it sayeth unto thee, inscribed on ye tablets of gold which come in a vision from the Worcester website,

"Check the gas supply working pressure at
the gas valve inlet point is no less than:
N.G. 18.5 mbar"

Thou hasn't got a corgi's chance in hell of getting that without very adequate supplies. Boiler uses 2.7cu m by the way, kev looked up the non-greenstar. So did your plumbers, perhaps, because the non-Greenstar Si's WOULD run on an undersized supply, (unofficially) even though they use more gas.

Gas meter outputs are specced to be 21mbar +/-2, so it'll be your luck that it's 19. You could get it measured, or even leaned on, but even at 23mbar you probably wouldn't make it, with 1mbar drop every 2.5 metres or so - remember the joints and the cooker.

Is this a terraced property? - you can put gas pipes along outside walls cos even in this weather, methane don't freeze. Or up the walls and through the loft. Or behind tasteful ceiling coving.

 

[DP]

Already the water is getting muddied.

Shame that engineers recomended by the manufucaturer can make a statement counter to what the manual says. Manual instructions are to be followed. That is official (part of gas regs)

There is a good chance even 22 may be undersized. If an installer cannot calculate pipe sizes for discharge, he should not be doing gas work.

 

[poppins]

Is this a terraced property? - you can put gas pipes along outside walls cos even in this weather, methane don't freeze. Or up the walls and through the loft. Or behind tasteful ceiling coving.

It's an end-terraced property, and luckily the meter is on the detached side. So it's good to know there are alternatives to digging up a concrete floor.

Which returns me to one of my original questions. Will an undergassed boiler simply underperform, or will it put it under more strain and cause it to fail rapidly?

In other words, is it essential to get the pipes replaced immediately?

 

[poppins]

If an installer cannot calculate pipe sizes for discharge, he should not be doing gas work.

True, but as the majority of the pipework is encased in the floor, it's not possible to determine the thickness of pipe all the way back to the meter, or to count the number of elbows and joints (without getting hold of the building specifications which I am going to try and get hold of).

Assuming it is possible to measure both the flow rate and the pressure at the boiler end (I know it's possible to measure pressure, don't know about flow rate), I now know what values to make sure he gets!

I may ask him for a quote to replace the piping as far as possible.

Thanks again.

 

[poppins]

If anyone's interested, I spoke to CORGI and Worcester-Bosch about this.

The CORGI support line said that it could cause an explosive ignition which could then eventually cause damage to the system.

The Worcester-Bosch support line said that if it was undergassed it would simply not work at all.

I'm hoping for the latter, because that means it will either work or it won't, and if it won't then we can come back to the engineer who said it would.

And even if there was an explosive ignition it would at least mean it would be a fault we'd notice straight away and again the engineer would be responsible.

 

[Bahco]

You ARE making a meal out of this

The Corgis have told you that you will need either 22 or 28 mm piping.

Get it sorted. End of.