Strange gas pressure drop

dl18sh · Tuesday at 8:09 PM

First of all, Im on a learning curve with this topic so any help/ guidance would be greatly appreciated. Thank you!

Long story short, boiler broken, PCB and gas valve replaced (was told that one might have short circuited the other). All working afterwards and engineer also did a service (certificate attached). However, he told us that “Gas supply to boiler under sized. 18mlb at meter & 9.5mlb at boiler on max rate”

The same engineer serviced and issued all-clear certificate last year so I’m shocked now that he said the pipework needs replacing and “happy to ring the office to give you a quote”.

I could be totally wrong but suspect:
1) a faulty gas valve was used
2) blockage in the pipework (it has always been fine since 2015, previous owner was a landlord and had to do certificate every year, until we bought in 2021 but something might have happened)

If 1 is likely, I’ll push for the engineer to come back and take a look. Fail that, I’ll get a second opinion from another company to get the 1st engineer to make his job right.

If 2 is likely, I’ll have to call the supplier to take a look?

Your advice on this would be appreciated. Many thanks in advance.

P/S: the gas rate (on high) in the attached certificate said 37 m3/h but I think he probably meant 3.7m3/h? If so, this appears to be within normal range, but how does that work given the pressure is low?

CountryFan · Tuesday at 9:03 PM

Supplier won’t do anything as it’s not their responsibility, it’s yours. Supply at the meter is only just under at 18, can now be 18.5mbar. If you’re getting 9.5mbar then something is definitely amiss. Do you know what test program was used? Gas rate definitely wrong as well.

Razor900 · Tuesday at 9:06 PM

It's nothing to do with the supplier.

That's a big boiler you have there. If you have less than 25 rads it's probably never getting to max rate anyway.

What size is the gas pipe and how far does it run?

dl18sh · Tuesday at 9:43 PM

Thank you for the responses.
I’m not sure what test he ran to be honest, though I understand he tested on max rate (full load).

Suppose I’ll have to measure the pipe on the right of the meter in picture (one that goes to my house)?

We have only 7 radiators, 2 hot rails in the bathrooms and 1 underfloor heating for a c. 350sqft open plan kitchen. So definitely less than 25. The boiler also heats our water cylinder.

On our full use, both heating and hot water on, the flame icon on the boiler has always remained 1/4 of the bar, never reached above 1/3 (not that I’ve seen).

Been running for 10 years with no issues. Last year, the supplier changed to a smart meter (but don’t think this has anything to do with it?). The meter is about 9-10 meters to the boiler.

fixitflav · Wednesday at 3:04 PM

CountryFan said:
Supplier won’t do anything as it’s not their responsibility, it’s yours. Supply at the meter is only just under at 18, can now be 18.5mbar. If you’re getting 9.5mbar then something is definitely amiss. Do you know what test program was used? Gas rate definitely wrong as well.

I thought pressure out of the meter was 21+/-2mb, so minimum 19mb.

fixitflav · Wednesday at 3:07 PM

dl18sh said:
Long story short, boiler broken, PCB and gas valve replaced (was told that one might have short circuited the other). All working afterwards and engineer also did a service (certificate attached). However, he told us that “Gas supply to boiler under sized. 18mlb at meter & 9.5mlb at boiler on max rate”

The same engineer serviced and issued all-clear certificate last year so I’m shocked now that he said the pipework needs replacing and “happy to ring the office to give you a quote”.

Sounds like a try-on to me. For one thing, if those are the pressures he says are a problem, you'd expect them to be noted on the report.

denso13 · Wednesday at 3:17 PM

fixitflav said:
I thought pressure out of the meter was 21+/-2mb, so minimum 19mb.

Should be between 18.5 and 23mb, but as it was less than 18, the gas guy should have reported it.

fixitflav said:
Sounds like a try-on to me.

Doesn't read right, that's for sure.

fixitflav · Wednesday at 3:22 PM

denso13 said:
Should be between 18.5 and 23mb, but as it was less than 18, the gas guy should have reported it.

The minimum must have changed then, 21+2 = 23mb still

denso13 · Wednesday at 4:09 PM

fixitflav said:
The minimum must have changed then, 21+2 = 23mb still

Yes, https://www.kane.co.uk/news/new-igem-guidance-on-domestic-gas-meter-supply-operating-pressure

Harry Bloomfield · Wednesday at 4:12 PM

dl18sh said:
1) a faulty gas valve was used

It cannot really be that, the pressure drop is measured at the input to the gas valve, if he's blaming the pipework. It might be the gas valve if the 9.5 is the pressure at the output side of the gas valve.

Best thing, is read the manual, so you know where the test points are, which is which, and watch the readings over his shoulder.

fixitflav · Wednesday at 4:20 PM

denso13 said:
Yes, https://www.kane.co.uk/news/new-igem-guidance-on-domestic-gas-meter-supply-operating-pressure

Is the maximum loss between meter and boiler still 1mb?

Daveydub · Wednesday at 4:21 PM

37 m3hr may have a missing decimal point or perhaps he forgot to change it to 37kw.
Seems a more likely mistake to me and possibly it wasn't gas rated.
Does 22mm go all the way to the boiler?

denso13 · Wednesday at 4:32 PM

fixitflav said:
Is the maximum loss between meter and boiler still 1mb?

Yes.

CountryFan · Wednesday at 5:14 PM

fixitflav said:
I thought pressure out of the meter was 21+/-2mb, so minimum 19mb.

As pointed out, it was changed recently.

dl18sh · Wednesday at 6:27 PM

Harry Bloomfield said:
It cannot really be that, the pressure drop is measured at the input to the gas valve, if he's blaming the pipework. It might be the gas valve if the 9.5 is the pressure at the output side of the gas valve.

Best thing, is read the manual, so you know where the test points are, which is which, and watch the readings over his shoulder.

Thanks. I did not get the chance to check the reading when he was doing the work. But you are right, the pressure comparison were 1) at the meter and then 2) at the input to the boiler. At boiler, the 9.5mbar is very low vs manufacture recommended pressure ~17mbar (Vaillant EcoTec plus 637).

What I’m struggling to understand is, if pressure is so low as he said, how can the boiler still deliver burn rate 3.7 m3/h (under max load). i.e. the volume of gas delivered to the boiler under max load is still well within manufacture range (max 3.8 m3/h) despite the pressure being just over half of manufacturer’s working required level (9.5mbar vs 17mbar)?? Or is there no relationship between volume burn and pressure?

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