Gas pressure question

[Wormwood]

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.

 

[ShaunCorbs]

Do you know what we're the pressures ?

 

[Wormwood]

Thanks for the reply Shaun.

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

 

[ShaunCorbs]

Thanks for the reply Shaun.

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

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 ?

 

[Wormwood]

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

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

 

[ShaunCorbs]

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

 

[Wormwood]

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

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

 

[ShaunCorbs]

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

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

 

[Wormwood]

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

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

 

[townfanjon]

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

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

You would not have known .

 

[ShaunCorbs]

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

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

 

[Wormwood]

You would not have known .

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.

 

[Wormwood]

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

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.

 

[Chuck]

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.

 

[snowhead]

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.

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

 

[Wormwood]

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.

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!

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.

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

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

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.

 

[Wormwood]

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.

 

[snowhead]

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.

 

[Wormwood]

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.

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).

 

[king of pipes]

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

 

[Wormwood]

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

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.

 

[Wormwood]

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).

 

[ShaunCorbs]

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).

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

 

[GH77]

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

 

[king of pipes]

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