15mm gas supply to new 30kW system boiler - OK?

[Rory]

As part of our house refurb I had the boiler replaced and a pressurised hot water cylinder fitted. Builder's CH people used Glowworm Energy 7 30S system boiler, and mounted it very neatly above the cylinder.

I was a bit surprised to see it piped in 15mm from the 22mm that comes through the wall nearby, to also feed a gas fire and a hob. Fitter insisted it'll be OK because "it isn't a combi" - I don't get that as it's the same output as many combi's?

It also strikes me as a bit short-sighted - when the boiler next gets replaced if one is fitted that needs 22mm then the pipe run will mean the cylinder has to be removed.

 

[Riley]

To be fair I’d speculate that a 30kw boiler will be well oversized any way and would likely be range rated down to an appropriate output for the property

 

[miketurner201]

Plumber had gone for a 24kw now as that’s the same as the old one.

 

[Rory]

Sorry for delay in replying - had floor screed done and couldn't walk on it to get to boiler!

Benchmark sheet has Gas rate as 3.42 cu meters/hr and Dynamic inlet pressure at 21mbar.

As for witnessing the test I asked him and he said he'd give me a shout but then said he forgot! To be fair, that's consistent - a few things he's just gone ahead and fitted without checking position with us, even when specifically asked to.

However I'm making a bold assumption that he wouldn't fake the results as he'd get caught out the first time anyone else tested it?

 

[Last Plumber]

Sorry for delay in replying - had floor screed done and couldn't walk on it to get to boiler!

Benchmark sheet has Gas rate as 3.42 cu meters/hr and Dynamic inlet pressure at 21mbar.

As for witnessing the test I asked him and he said he'd give me a shout but then said he forgot! To be fair, that's consistent - a few things he's just gone ahead and fitted without checking position with us, even when specifically asked to.

However I'm making a bold assumption that he wouldn't fake the results as he'd get caught out the first time anyone else tested it?

It would come to light during the first service as you suspect.
Unless he does it!

 

[Chuck]

You can ask Gas Safe to inspect the completed installation if you have reservations about it. If they find any issues the installer will be obliged to correct them.

 

[Rory]

CH guy was here today fitting the hob. I said the boiler was niggling me and asked him to show me.

He stuck his manometer on the boiler and showed me it reading 23mbar with the boiler apparently running "flat out".

 

[miketurner201]

Plumber had gone for a 24kw now as that’s the same as the old one.

Sorry I posted this in the wrong thread.

 

[Last Plumber]

CH guy was here today fitting the hob. I said the boiler was niggling me and asked him to show me.

He stuck his manometer on the boiler and showed me it reading 23mbar with the boiler apparently running "flat out".

What was it at the meter with the boiler running flat out?
The boiler will be designed to run at 20mb inlet pressure. You need to know what it is at the meter outlet when it is running flat out and what it is at the appliance. This will tell you the drop across the supply pipework.

 

[Rory]

It was at the boiler.

The trouble is, I know enough to feel uncomfortable about this, but not enough to argue with the CH guy, who clearly thinks I'm being completely ridiculous and there's absolutely no question in his mind that it's perfectly fine.

Is 23mbar at the boiler normal? I thought it was 21mbar typically.

I'm simply going off the tables that say the length plus bends etc of the 15mm tube can't carry enough gas for the boiler's max demand.

 

[Last Plumber]

It was at the boiler.

The trouble is, I know enough to feel uncomfortable about this, but not enough to argue with the CH guy, who clearly thinks I'm being completely ridiculous and there's absolutely no question in his mind that it's perfectly fine.

Is 23mbar at the boiler normal? I thought it was 21mbar typically.

I'm simply going off the tables that say the length plus bends etc of the 15mm tube can't carry enough gas for the boiler's max demand.

Typical U6 Meter on low pressure domestic service would be expected to be 21 mbar outlet working +/- 2 mbar.
They can be different, this is what is typical/expected.
You would expect (by design) a drop of 1 mbar meter to appliance working. This too can be different dependent on a number of factors but still be deemed acceptable. You'll have to trust me on that. Not got time to go through the technicalities.

You obviously have concerns. In my opinion you need a second opinion or to make it official, you would need to contact Gas Safe. If they do come to inspect the work, they will want the installer on site during the visit so you might want to discuss this with him and explain why you are considering it. Just to give him chance to go through it with you in enough detail to put your mind at ease.

 

[Rory]

Typical U6 Meter on low pressure domestic service would be expected to be 21 mbar outlet working +/- 2 mbar.
They can be different, this is what is typical/expected.
You would expect (by design) a drop of 1 mbar meter to appliance working. This too can be different dependent on a number of factors but still be deemed acceptable. You'll have to trust me on that. Not got time to go through the technicalities.

You obviously have concerns. In my opinion you need a second opinion or to make it official, you would need to contact Gas Safe. If they do come to inspect the work, they will want the installer on site during the visit so you might want to discuss this with him and explain why you are considering it. Just to give him chance to go through it with you in enough detail to put your mind at ease.

Thanks for that, appreciate it.

I think I'm just going to live with it. It's become apparent that replacing the gas pipe would not be the drama I thought it would as I insisted that I wasn't happy with the top edge of the cylinder pressing into the gas pipe - the fitters solution was to drain the cylinder, undo its connections and move it slightly.

I know it's true that the boiler will rarely run flat out - I just can't get my head around the gas carrying capacity of that length of 15mm tube seems miles below the boiler's max demand.