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Discuss Gas pressure question in the Gas Safe Register Forum - Public Forum area at

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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 :)).

  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

    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 Active Member

    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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