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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.
 
Any pictures of the install ?

Also depends on length / run
 
By my calcs, if it is less than around 2.5 meter run including losses for bends, fttings, valves etc. It should be OK.
I haven't seen it and I don't know where the other things you mention tee off.

If there is 22mm nearby as you said, I can't see the installer dropping to 15mm unless they were confident it would work.

There will be a good decade before the next boiler hopefully. Who knows what the future holds?

Are there pictures?
Are there figures in the benchmark form?

Whether it is a combi or not makes no difference. It is the gas rate and pressure drop that governs the required pipe size.
 
Can't get at it for a useful picture, but this is the boiler end, with the top of the cylinder at the bottom of the picture:

IMG_1781.jpeg


It's a swept bend in the corner, then down behind the cylinder, a couple of dog-legs then into the 22. Meter is the other side of the wall in the picture.

Close as I can get,, the total 15mm pipe length is 1.55 metres. What I don't know is the effect the dog-legs, bends and elbows have - or the gas connection, which the fitter pointed out is 15mm anyway.
 
It is only a short run so it may be fine.
The only way to 'know' is to test the drop across the run. He will more than likely have tested it when he commissioned the boiler.
There is no point in over sizing something if you don't need to.
 
Thanks - it's "may be fine" part that bothers me.

The boiler hasn't been commissioned yet. The way the pipe is routed I'd have erred on the side of being absolutely certain!
 
Thanks - it's "may be fine" part that bothers me.

The boiler hasn't been commissioned yet. The way the pipe is routed I'd have erred on the side of being absolutely certain!
I wasn't meaning that to sound flippant!
It may be fine meant, it might well be that the loss from meter to appliance is acceptable. i.e. within tolerances allowed by current rules, regs and standards that we all work to. So long as the pressure drop is within the limits, then it will be fine!

That's not the same as 'it'll do'! which is how I think you took it.

Through any length of pipe you will have a pressure loss through frictional resistances. That goes for gas, water, whatever. This drop or loss is measured during commissioning, servicing, fault finding etc. So long as it is an acceptable amount and does not effect other appliances, then it is fine.

If your appliance has not been commissioned, then the installer won't 'know' whether or not it is acceptable but he will have a good idea through experience or calculations. As I said previously, there is no point over sizing something. When it is commissioned, you will 'know' whether the pressure loss is acceptable or not.

Hope that makes more sense.
 
Thanks - no problem, did understand what you meant. My point was that, especially bearing in mind how short yet awkward the run is, if you weren't 150% certain it was going to be OK then why not just run it in 22mm?

I suppose that's the point, the fitter is 150% certain, and I know enough to wonder about it, but not enough to be able to argue with him. My concern is the effective length of the pipe vs the maximum demand of the boiler makes it pretty marginal.

When I very gently raised this the response I got was "it'll be fine because it's a system boiler." OK, I realise that it'll not often be running flat out like a combi does but for a given power rating won't the gas consumption be the same?
 
As part of commissioning the boiler is run full pelt and gas pressure is measured. If it meets spec, it’s fine. End of. There are boilers running on metres of 15mm around here.
 
Thanks - no problem, did understand what you meant. My point was that, especially bearing in mind how short yet awkward the run is, if you weren't 150% certain it was going to be OK then why not just run it in 22mm?

I suppose that's the point, the fitter is 150% certain, and I know enough to wonder about it, but not enough to be able to argue with him. My concern is the effective length of the pipe vs the maximum demand of the boiler makes it pretty marginal.

When I very gently raised this the response I got was "it'll be fine because it's a system boiler." OK, I realise that it'll not often be running flat out like a combi does but for a given power rating won't the gas consumption be the same?
It doesn't matter whether it is a regular boiler, system boiler or combi boiler. The maximum gas rate is used to test the drop. If they pass that, that's it!

You could be worrying for no reason.
 
Just returning to this - boiler was commissoned today and Benchmark form done. He's got the max gas rate as 3.4 cu metres/hr, which is same as figure I'd found. He says it tests fine, but there's still the insistence that, despite the max output being the same, it's not the same as a combi as system boilers never run flat out....?

It's just niggling at me that my understanding (which I'm happy to be put right on) of the amount of gas that could possibly get through that effective length of 15mm tube is somewhere less than 3cu metres/hr.

I'm more annoyed with myself than anything else for not insisting from the start it should be done in 22mm - I'd misunderstood and thought that was standard practice now, but apparently that only applies to combis.
 
Did he do a pressure loss ?
 
Should be gas inlet pressure
 
As I said earlier in the thread, it is the max gas rate we use - in this instance - to size pipework. Not the boiler type.

Can you not ask to witness the tests or get a second opinion?
A second opinion will cost something but not much compared to your anxiety.
 
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
 
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?
 
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!
 
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.
 
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".
 
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.
 
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.
 
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.
 
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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.
 

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