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Discuss Gas pressure question in the Gas Safe Register Forum - Public Forum area at UKPlumbersForums.co.uk.

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  1. Wormwood

    Wormwood New Member

    I've had a tech survey for a new boiler and they reckon the gas pressure (at the boiler) is too low. Could this be caused by an old/knackered gas meter?

    My meter is a 1985 Parkinson Cowan. National Grid put a new regulator on and the pressure immediately went up by 4mbar - but they didn't change the rest of the meter (i.e. the big bit :)).

    TIA.
     
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Do you know what we're the pressures ?
     
  3. Wormwood

    Wormwood New Member

    Thanks for the reply Shaun.

    I think they were 19mbar before the regulator change and 23 after it.
     
  4. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    That would be standing and can't see the meter affecting that much as there designed to give no restriction or very little

    Would say it's down to pipework from the meter

    May I ask what's your existing boiler and whats the new one your looking at ?
     
  5. Wormwood

    Wormwood New Member

    What could be wrong with the pipework? The existing boiler has run perfectly happily with it for 30 years. :confused:

    I don't know what the new boiler will be.
     
  6. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Could be a bigger kw requiring more gas hard to say really
     
  7. Wormwood

    Wormwood New Member

    No, they said it was too low regardless of the boiler's kw. They reckoned a 22mm pipe would give more mbars.
     
  8. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Yes we're only allowed max 1.5 mbar drop from the meter to the appliance working
     
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  9. Wormwood

    Wormwood New Member

    By 'appliance working', do you mean the measuring device (e.g. this one) is connected to the boiler itself, while the boiler is running?
     
  10. townfanjon

    townfanjon Trusted Plumber GSR Top Contributor!!


    You would not have known .
     
  11. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    yes under full load and this is how i normally do it

    turn boiler and any other appliances on on to full load / high burn
    test pressure at meter
    test pressure at boiler (allowing for restriction through the gas valve listed in the manufacture instructions)

    say you have a inlet meter working pressure of 21 mbar
    at the boiler you have 18 mbar working
    you look in the instructions and your gas valve has a restriction of 2 mbar

    21 - 2 - 1.5 = 17.5 mbar max so your pipework size is correctly size
     
  12. Wormwood

    Wormwood New Member

    No, but if the pressure is high enough for my existing boiler (Glow-Worm), I don't see why it's not high enough for a new boiler (any ordinary/standard replacement).

    The Glow-Worm has only ever cut out twice in the 10 years I've owned the house and that was in extremely high winds - the wind blew the pilot light out by coming in thorough the large (cage type) flue, which is an exposed place on the outside wall. The boiler has never cut out due to low gas pressure.
     
    Last edited: Jul 16, 2017
  13. Wormwood

    Wormwood New Member

    How do I find out the figure for the bits I've highlighted red Shaun?

    I should mention that the chap who measured the pressure at the boiler did it twice on two different days - and he got two completely different readings. This was using the same digital measurement device. Why would that happen?

    I think the readings were 11 and 16mbar (boiler working) - but that was before National Grid changed the regulator (which raised it by 4mbar at the meter outlet).

    I'm wondering if there's a partial blockage in the pipe between the gas meter cupboard and the boiler (distance is around 12 feet). I did think of getting someone in to blow compressed air through the pipe - i.e. disconnect at the regulator & boiler ends and attach a high pressure air hose to one end.
     
  14. Chuck

    Chuck Top Contributor!!

    It's not common, but gas pipes sometimes get partially blocked by water. Have there been gas main repairs in the area in the recent past?

    Whatever the problem, the solution is to get a GSR in to diagnose and fix it. Do not be tempted to try DIYing this one.
     
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  15. snowhead

    snowhead Well-Known Member

    Air and gas in the right mixture (with added ignition) = potential explosion.
    No GSR would carry out your request.
    Only a GSR can break the pipework.

    The meter doesn't belong to Nat Grid Gas, now called Cadent.
    Your energy supplier owns it and would need to be contacted if there is a suspected problem.

    The new boiler would probably work quite happily on a lower pressure, the manufacturers spec would probably show that, but all appliances and pipework installed today have to conform to the Regulations in force today.
    As above that means no less than 1.5mb drop
     
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  16. Wormwood

    Wormwood New Member

    Part of the pavement/road was dug up last year - I didn't pay any attention to it though, so I'm not sure if it was gas, H2O or electricity.

    As far as I know, no other house in the road has had to resort to swapping to a 22mm pipe when they've had a new boiler fitted - hence my suspicion of something partially blocking my pipe, either upstream or downstream of the meter. Or, the meter itself is restricting gas flow (more than meters normally do).

    I'm not tempted to DIY it. I know what gas can do when it goes off!

    How else can they check if the pipe is partially blocked then?

    The chap who tested the pressure at the boiler did not test the pressure at the meter.

    The other chap tested the pressure at the meter (when he changed the regulator) but did not test the pressure at the boiler.

    In other words, both points have not been tested at the same time. Hence, I have no idea whether the drop from meter to boiler is more or less than 1.5mb. All I was told is that the pressure at the boiler end of the pipe is too low and a 22mm pipe would solve it.
     
    Last edited: Jul 16, 2017
  17. Wormwood

    Wormwood New Member

    My current plan is this.

    1. Ask the supplier to change the whole meter for a new one.

    2. Get someone in to measure the gas pressure in and out of the meter. Then measure the working pressure at the boiler.

    Sounds reasonable to me.

    :):):)
     
  18. snowhead

    snowhead Well-Known Member

    I'm out after this, but you'll end up with 22mm up to the new boiler whoever fits it and whatever size it is.

    Has anyone checked whether you have Earth Bonding to the gas pipework?
    Even tho' your boiler may have worked fine without it for 30yrs, you'll still need to have it if it's not in place.
     
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  19. Wormwood

    Wormwood New Member

    Why will I end up with 22mm?

    Yes, there is earth bonding on gas & water pipes and it's ok (it was checked & certified by an electrician in June).
     
  20. king of pipes

    king of pipes Trusted Plumber GSR Top Contributor!!

    Do not attempt anything on your gas supply contact a GSR he will diagnose your problem and if you should need a vist from cadent he will arrange another vist . cheers kop
     
  21. Wormwood

    Wormwood New Member

    See post 16 paragraph 3 :)

    I've worked on a gas rig in the North Sea so I'm not tempted to do anything myself gas-wise.
     
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  22. Wormwood

    Wormwood New Member

    I still don't see why the pipe has to be 22mm as long as the pressure drop is within regs (as per Shaun and Snowhead's advice).
     
  23. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    The only time is if it's out of spec e.g. More than allowed pressure drop
     
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  24. GH77

    GH77 GSR Top Contributor!!

    If the old boiler has a pilot light then it will be an atmospheric burner, it will only require enough gas pressure to make Burner pressure, for example 10mb, your new boiler will be a zero governer, these ideally require 20mb inlet working, but depending on the boiler can be as low as 14mb, more usual is 16.5 to 18mb. If your meter regulator is supplying 19-21mb working pressure and you then don't have enough working pressure at the boiler, then your Pipework is undersized. The engineer who carried out the survey should have carried out a pipe sizing exercise to determine if the existing pipe is suitable, he has said it is not and requires upgrading for a new boiler, if he hadn't done this and just fitted a new boiler, he would be liable to correct the installation error at his own cost. Sounds like he is a professional doing a good job, I would suggest you follow his advice
     
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  25. king of pipes

    king of pipes Trusted Plumber GSR Top Contributor!!

    Providing the pressure drop is within the regulations then you are ok , if not then it will need to be addressed i am afraid ,when you upgrade any proffesional Gsr would upgrade a 30year old gas supply when fitting a new modern condensing boiler any debris rust or otherwise would not be a issue then and you will have a supply correctly sized and which will last the life of the boiler and longer regards kop
     
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  26. Wormwood

    Wormwood New Member

    Ok, thanks Shaun - I understand. What do you think of my plan in post 17?

    Thanks for that explanation GH77.

    The pipe coming out of the meter is 22mm, so it reduces to 15mm somewhere inside the house. It would be really good if I could find out exactly where - maybe it's right next to the boiler (the 15mm disappears into the plaster so I can't tell).

    Btw, there's a rust-coloured deposit all over the inlet pipe to the meter. I wonder if it's got inside the pipe as well. Hmm.

    Ok, thanks Kop.
     
  27. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    I would get no 2 done first and see what you get
     
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  28. Matchless.plumb

    Matchless.plumb Trusted Plumber Top Contributor!!

    I think rules have changed 1mbar drop max. From meter to appliance 1mbar drop only!
     
  29. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Still 1.5mbar max
     
  30. GH77

    GH77 GSR Top Contributor!!

    IMG_5893.PNG Depends where your pressure test point at the boiler is, whether you've got one before the boiler or using the test point on the Gas Valve, picture paints a thousand words
     
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  31. Chalked

    Chalked Plumber GSR

    I think this thread should be closed.
    There is too much gas related info being given to a diy'er who should just employ a good gsr to install the new boiler and update the supply pipework as needed.
     
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  32. GH77

    GH77 GSR Top Contributor!!

    He already has, just reassuring him that his GSR is correct, why he's correct and that he's not being ripped off
     
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  33. townfanjon

    townfanjon Trusted Plumber GSR Top Contributor!!

    Agree with chalked , this should have been closed yesterday
     
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  34. Wormwood

    Wormwood New Member

    I am NOT a DIYer!!

    I've already said several times that I have no intention of doing it myself and that I have and will use a qualified gas installer.

    Read posts 16 & 21!

    Is that clear enough for you?

    I will not say it again.
     
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  35. Wormwood

    Wormwood New Member

    Yes, I think you're right. Then no 1 if it's still too low. (My meter really is ancient, spiders crawling out of it, etc, etc).

    Btw, I reckon the 22mm-15mm reducer is closer to the boiler than I thought (I had a closer look last night). The 22mm comes out of the meter and goes straight back through the wall horizontally. After 10 inches, it disappears behind the plasterwork inside the lounge.

    Here it must either a) turn vertical until it reaches 1st floor joist level - or b) go off in another direction.

    Assuming a) is correct, it must turn horizontal again and run through the joists, over the hall, over the downstairs toilet, and into the kitchen, where the boiler is. Then it turns vertical again (so it's now pointing downwards), reduces to 15mm and runs down inside the plaster to the boiler.

    All I have to do is find the point where the reducer is - my guess is directly above the boiler at 1st floor joist level.
     
    Last edited: Jul 17, 2017
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