Huge gas pressure drop between meter and boiler. Help!

[fixitflav]

Ignore the DIYers advice, if the gas pressure has suddenly dropped, then there's a reason for it.

But has it suddenly dropped, or were the 2 sets of measurements looking at different things, with and without flow?

 

[FiremanT]

But has it suddenly dropped, or were the 2 sets of measurements looking at different things, with and without flow?

It has not “suddenly” dropped, the earlier identical readings were almost certainly fake.

Non combi boilers need pipe work a LOT smaller than combi’s, and it is rare not to need to upgrade.

The only way that you would get identical figures would be as standing pressure (nothing firing)

 

[FiremanT]

It is potentially bad, depending on the OD. Steel pipe is much thicker walled than copper, so less space for gas to flow.

It is bad, simples.

look at the glow rates for iron, and it may well only be 3/4” OD

 

[FiremanT]

I am certain that the plumber just connected up the old pipes and didn’t check to see anything else as seemingly it wasn’t an issue in the past. Easy work and payday but he would argue that it would have been more expensive to change the pipe work etc.


The pipe that feeds off the meter must be iron as a weak magnet stuck to it. Is that good or bad? Other than the height clearance why do you think he installed
incorrectly. He will argue he just replaced the boiler in situ.

Your 30kw combi is probably at least twice the consumption of your old boiler. He cannot argue that he was just connecting a boiler, nor can he ignore the rules to save you money, even if you demand it and even if you sign a disclaimer and for you to accept responsibility.

 

[FiremanT]

Does one need to be to make a perfectly sensible post as he made above. What do you think, in your personal opinion, was wrong with what he suggested?

Everything is not a specific answer. Try to be specific please...

I apologise - point one was almost certainly correct , the pipework is undersized . The rest is nonsense

 

[Harry Bloomfield]

I apologise - point one was almost certainly correct , the pipework is undersized . The rest is nonsense

Too early to offer a firm opinion, there is a lot the OP seems so unsure of.

 

[FiremanT]

Too early to offer a firm opinion, there is a lot the OP seems so unsure of.

Maybe so, but I do actually know what I am talking about, and the Ed e are few actual options.

90% of comments on this thread are either guesswork or complete nonsense.

Even the original installer believes the pipework is undersized! He cocked up , I believe, and is now trying to get the OP to pay for new pipework!
OP: phone Gas Safe and ask for an inspection.

 

[gas112]

.


As I understand it, pressure after the meter should be 21+/-2mb, so 17mb would be non-compliant and the gas supplier should rectify it.

Nope they only have to supply 19mb at ecv losing up to 4mb across meter so can be as low as 15mb at meter outlet without them having to do anything

 

[FiremanT]

It was installed 2 years ago, and recently serviced by the plumber that installed it. We don't know who serviced it last year, when the 20mb at meter and boiler were obtained, but it's a fair bet it was the same guy. If the installer failed to meet the 1mb drop reg perhaps he should be pulled up, but unless Gas Safe or somebody hears about it, I don't suppose anything much will happen.
Treating it as a "come across" job, where excessive pressure drop is only NCS, presumably it's OK.


As I understand it, pressure after the meter should be 21+/-2mb, so 17mb would be non-compliant and the gas supplier should rectify it. But if it did fall to 17mb, with pipe drop 20-13.5 = 6.5mb, so something like 11mb at the boiler, the boiler output would be down (unless it has a low-pressure cutout, I wouldn't know)

I was waiting for precisely that comment, but missed it earlier!
As per 112, it can go down to 15mb.
Which is why the 1mb should be observed. With a meter pressure of 21mb, a 4mb loss will probably have no real effect. If the MP drops to, say, 16mb due to an incident or peak usage, then it can seriously affect other, particularly non Flame failure protected, appliances.

 

[boolie]

@davecon70 can you post pictures please? Of the boiler and any pipework

My money's on the installer having screwed up in the first place. He probably didn't do a pipe size calculation and just hooked it up to the old supply without checking.

 

[fixitflav]

t has not “suddenly” dropped, the earlier identical readings were almost certainly fake.

Exactly, that's the point I was making

 

[fixitflav]

Nope they only have to supply 19mb at ecv losing up to 4mb across meter so can be as low as 15mb at meter outlet without them having to do anything

OK thanks. I always understood the regs were as I said, but not for the first time, I stand corrected. I think somebody should tell the boiler manufacturers! Many of them say pressure at boiler inlet MINIMUM (their caps) 20mb. I believe Vaillant are in a minority in giving an actual requirement.

But is the consensus that the OP needs to do anything, or is it considered NCS?

If he does, and assuming the buried 8m section is 1” NB (OP – can you confirm the OD?), giving about 0.15mb drop at 3.2m3/h, replacing the 5m of 15mm pipe with 22mm should do the trick. Estimated drop in that section about 0.3mb, so total well within the 1mb allowed. That might not be too big a job.

Edit - before doing anything, a good idea to install a tapping point on the boiler inlet pipe, and do some proper drop tests.

 

[denso13]

90% of comments on this thread are either guesswork

100% are guesswork. It needs checking on site to be definitive.

 

[Harry Bloomfield]

100% are guesswork. It needs checking on site to be definitive.

Of course, everyone's submissions via the forum are entirely guesswork - how could they possibly be anything else without Mk I eyeball on site?

 

[denso13]

Of course, everyone's submissions via the forum are entirely guesswork

Yes, it's amazing though how many threads jump to the assumption the installer is useless. Maybe he was, maybe the OP is mistaken (through no fault of his/her own), but there is only one way to be sure.