Low gas pressure during boiler full load test

[z2chris]

Hi, I am a homeowner but caught between a rock & a hard place.

I am trying to get a Vaillant ecoTEC 630 plus serviced but the gas safe engineer & Vaillant engineer say one thing, whilst the SGN engineer says another. I do not know how to proceed and would value some informed advice.

The rock – a Vaillant approved gas safe engineer came to service the boiler but found low gas pressure (1-2mbar) at test point during full load check (boiler set to max heat) with 5 ring gas-hob also on full and said that the boiler is unsafe to use. Still under guarantee so Vaillant engineer came & replaced gas inlet value but then said it still has too low gas pressure (7mbar) and is unsafe to use. The Vaillant maintenance instructions specify 13-23mbar as permissible so I understand their conclusion.
The hard place - I next contacted SGN who came and checked the gas supply-side & meter. They said that was all ok and at the expected & acceptable pressure. SGN also gave opinion that the 3 metre run of 22mm pipe from meter to boiler, down to 10 cm run of 15mm pipe into boiler inlet, should be an ok sizing.

The SGN engineer said the boiler was perfectly safe to use and that SGN had instructed boiler manufacturers & installers not to perform full load tests any more because the recently replaced 20mm plastic gas pipe from the road to the house would not support a full load test with boilers like this & would always show low pressure under a full load test regardless of meter-to-boiler pipe capacity. He also said that because the boiler would never run at full load in real life it was not necessary to perform this test from a safety point of view.

When in normal operating mode, everything is fine. But not during full load test. Who is right here? I am at a loss how to proceed. SGN say everything is fine but I can’t get it serviced because Vaillant & the independent gas safe engineer say it is not.

 

[ShaunCorbs]

That’s bollox from the sgn need to do a full test as it’s gas / manufacturer regs

It does run at full load on hot water etc

I’ve had it before the pipe was full of water / crap from them putting it in inside the old pipe etc

 

[Deleted member 120897]

Was a meter working pressure test carried out?

 

[z2chris]

Was a meter working pressure test carried out?

Hi ChrisB1982, I believe it was. The original engineer mentioned 17mbar at the meter, suggesting that was a little low but should be workable. The SGN engineer also tested at the meter, but didn't share the result

 

[Deleted member 120897]

Hi ChrisB1982, I believe it was. The original engineer mentioned 17mbar at the meter, suggesting that was a little low but should be workable. The SGN engineer also tested at the meter, but didn't share the result

We were always taught 21mbar at the meter, +/- 2mbar. I’ve recently found out it can be as low as 18.5 mbar, so, imo 17 is too low to start with. I would ask to speak to someone higher up the food chain at SGN. If you feel this doesn’t get you anywhere, then I would be speaking to gas safe. It’s not performing as per the manufacturers instructions (mi’s) and is likely affecting the safe operating performance of the boiler

 

[fowlerboi]

As above.

Working pressure at the meter needs to be taken, if its 21mb (+/- 2mb) then that's fine and continue with the next step. If its lower than it should be then the gas board need to fix it. I've had an engineer tell a colleague its because we fitted too big a boiler (35kw) quite frankly I don't give a Rubbish its their job to get the correct pipework to the meter, if they have to dig it up they have to dig it up, they're responsible for it

Working pressure at the boiler inlet, this should be within 1mb of the working pressure I talked about above (some boilers allow a certain drop Eg. Worcester allow an additional 1.5mb because the test point is at the gas valve.) If this is lower than it should be the installation pipework is the wrong size. If its OK and then with the hob running its too low, I would suggest incorrect pipe sizing

 

[z2chris]

As above.

Working pressure at the meter needs to be taken, if its 21mb (+/- 2mb) then that's fine and continue with the next step. If its lower than it should be then the gas board need to fix it. I've had an engineer tell a colleague its because we fitted too big a boiler (35kw) quite frankly I don't give a Rubbish its their job to get the correct pipework to the meter, if they have to dig it up they have to dig it up, they're responsible for it

Working pressure at the boiler inlet, this should be within 1mb of the working pressure I talked about above (some boilers allow a certain drop Eg. Worcester allow an additional 1.5mb because the test point is at the gas valve.) If this is lower than it should be the installation pipework is the wrong size. If its OK and then with the hob running its too low, I would suggest incorrect pipe sizing

Thanks for your advice and many thanks also to ChrisB1982. This is very helpful.

I have been looking up information around what has been posted and this makes sense. I will go back to the original engineer tomorrow and ask him to visit me again to re-measure & write down the working pressure at the meter and how much it drops through to the boiler.

It may be that the SGN engineer improved something when he was here (he did do things with the regulator on the meter), but simply didn't tell me. If not, then at least I will have some firm measurements to go forwards from. It is sounding like having a within-range working pressure at the meter is a good place to begin.

 

[Deleted member 120897]

Here is the information relating to a recent change (2022) in the industry which is aimed at all engineers, so sgn should be aware of it.

 

[gmartine]

Absolute cock & bull from SGN, think about raising a complaint if you don't make any reasonable progress.