Inlet pressure confusion

[Michael R]

Apologies for asking a question I realise no-one can answer for sure without actually doing their own measurements, but as a confused householder who is being told completely different things by different gas engineers, I just wondered if anybody could offer a suggestion on how in theory this might happen.

We had a very well-known boiler company's in-house engineer service our boiler last week. He reckoned the gas inlet working pressure was only 6mb, compared with the 21mb he measured at the meter. My inexpert googling suggests that 6mb is a seriously low figure; the boiler manual specifies a minimum of 15 for our model.

The next day, I got an independent engineer round (seemed very experienced and knowledgeable) to confirm the reading and advise on how to remedy it. He reckoned the pressure was 23mb at the meter and 22mb at the boiler, and that the boiler company guy didn't know what he was doing. I was delighted.

I informed the boiler company of this and they sent a different engineer out today. He took great pleasure in showing me that his colleague had been right and the inlet pressure was a mere 5.54Mb. So now I have two engineers each telling me that the other one doesn't know what they are doing.

I find it hard to believe that two different in-house engineers, both very familiar with our boiler (a popular model), would both get it wrong. So it looks like the other guy, who measured the pressure at 21mb, must have done.

Can anyone think of how this could possibly happen? Is it possible to measure this pressure the wrong way, or in the wrong place or something? I've read a bit about "standing pressure" and "working pressure" - could it be possible that an experienced engineer confused the two, or do the numbers not look right even for that?

Again, sorry for asking what is probably a daft question. Just trying to understand better what may have happened here, because obviously I'll be seeking a refund from whoever has cocked it up.

 

[bernardgreen]

If there is no gas flow along the pipe between the two points of measurement then the pressure difference between them will be very small if not zero.

 

[Gasinayr]

to get the correct " working " pressure the boiler must be switched on. if it is as low as 6mb then it should be switched off and a warning label attached

 

[Michael R]

to get the correct " working " pressure the boiler must be switched on. if it is as low as 6mb then it should be switched off and a warning label attached

This is the other thing that is confusing me. Though they have given me advice notices telling me to get the pipes checked (with the issue rated on "yellow", not "red"), both the in-house engineers told me verbally it'd be OK to carry on using it - despite the fact that the boiler installation manual states that if a pressure of 15mb cannot be achieved, the boiler should be switched off! I honestly don't know whether I can trust any of the three engineers who have been round. Currently trying to find a fourth...

 

[ianmcd]

He reckoned the gas inlet standing pressure was only 6mb,

you are confused, standing pressure is recorded when no appliances are being used, you actually mean working pressure, or operating pressure, they are very different, no way will you have 6mb standing pressure

 

[Michael R]

you are confused, standing pressure is recorded when no appliances are being used, you actually mean working pressure, or operating pressure, they are very different, no way will you have 6mb standing pressure

Thanks for spotting, yes I got mixed up there, it's the "gas inlet working pressure" he measured at 6mb. Edited to avoid confusion.

 

[ianmcd]

Thanks for spotting, yes I got mixed up there, it's the "gas inlet working pressure" he measured at 6mb. Edited to avoid confusion.

Trust me mate so many so called gas engineers get this completely wrong, 6mb is far too low, but doesnt always mean undersized pipework, ther are a few other causes of this

 

[jeff the gasman]

The manufacturers know better than your independent guy rest assured.

 

[CBW]

Did the independent engineer show you the result if the inlet working pressure? Was the boiler in operation at the time?

 

[fixitflav]

The next day, I got an independent engineer round (seemed very experienced and knowledgeable) to confirm the reading and advise on how to remedy it. He reckoned the pressure was 23mb at the meter and 22mb at the boiler, and that the boiler company guy didn't know what he was doing. I was delighted.

My guess is those measurements were taken with no flow ie boiler not firing. Are you sure the 6mb was at the boiler inlet, not the burner inlet (after the gas valve)?