Gas pressure at boiler 1/4millibars below min. What to do?

KTF

My new boiler has been fitted but it is coming in at 17 3/4 millibars instead of the required 18 millibars minimum. The pipe that comes into my flat is 22mm and 20 millibars at the gas meter but then drops to a narrower pipe when it comes into the flat which is the cause of the drop.

I have had two options suggested to me:

The first is to run a 22mm pipe outside of the flat up the wall directly to the boiler. This would give the required pressure but look awful and I am not sure if it can be done without gaining approval from the others in the block (its a leasehold flat).

The second is to trace the pipe that leads to the boiler as far as we can from the boiler to the meter (so far we have found approx 30 feet of it) and upgrade that length to 22mm in the hope that it will raise the pressure buy the required 1/4 millibar.

Option 3 (which I have just thought of and I dont know if it would be possible) is to replace the section of piping that we have round with say 30mm pipe for its length then drop it down to 22mm at the boiler. Would this work?

I am leaning towards taking the risk with the second option on the basis that the increase required is very small (and I really dont want a pipe running round the outside of the flat). The risk in taking the second option is that a whole day could be spent fitting the pipe only for the pressure to remain the same so an outside pipe would be required anyway.

I was wondering if anyone had an opinion on this and if they think replacing the small section of pipe would increase the pressure.

Thanks

Tim_L

Seems a bit odd to me. O level Physics would suggest that the pressure in the narrower pipe would increase, and then decrease again when you increase the diameter, but in a closed system you shouldn't actually lose pressure.

Are you certain there isn't a leak somewhere?

KTF

He leak tested the system before and after he started work and there are no leaks showing.

I am not sure how the pressure in gas pipes works to be honest. I would have expected a larger pipe to decrease the pressure but then I am not an expert.

KTF

I have looked at the instruction manual for the old boiler and it says that it needed 20mb to operate so it must have had that originally otherwise it wouldnt have passed the installation tests?

jimmyjim_uk

Is your gas meter in your flat?

Is your new boiler a combi boiler?

KTF

The gas meter is outside of the property next to the (shared) front door.

The boiler is a Worcester Bosch 24i Junior combi located in the bedroom on the second floor of the property (the meter being on the ground).

Edit: I called Transco to ask if the pressure could be increased at the meter and they got all excited and sent out an engineer as they thought there was a leak (which there isnt).

chrisw

I wouldn't have thought 1/4 millibar made much difference. Does the boiler work ok? If it does I would leave it as it is.

KTF

Neither would I. The boiler works fine but the manufacturers requirement is 18 - 20 millibar (which I believe the domestic gas supply should be to the meter) and he says that he cant sign it off until it reaches that level or the installation wont be certified.

jimmyjim_uk

KTF wrote:

The gas meter is outside of the property next to the (shared) front door.

The boiler is a Worcester Bosch 24i Junior combi located in the bedroom on the second floor of the property (the meter being on the ground).

Edit: I called Transco to ask if the pressure could be increased at the meter and they got all excited and sent out an engineer as they thought there was a leak (which there isnt).

Sounds to me like incorrectly sized pipework.

From the meter to the furthest appliance there should be no more than 1mbar pressure drop (Gas Regs). You have a pressure drop of 2 1/4 mbar which is very high. This would suggest to me that the pipework is undersized.

An option would be (if it is your own meter) to increase the size of the pipe after the meter to 28mm, also assuming you have a gas cooker, at the tee take 15mm to the cooker and 22mm to your boiler. Then reduce down to 15mm at the boiler.

The reason I asked if it is a combi is that they tend to a high gas demand and engineers tend to fit the same size feed pipe as the connection size.

Tim_L

Has the Transco guy been round then?

I would certainly try to get an independant measurement of the pressure at the boiler and the meter if at all possible, because I can't see how without a leak you could get a pressure drop of this size. I'd be faintly suspicious of the motives of the fitter who may be giving himself an easy day's work at full chargeout rates.

KTF

I am at work and wont be home till 7pm (which I told them when I logged the call) but they said they had to despatch someone within 1 hr as a low pressure report could be a leak. The call centre called me up about 15 mins after I logged the call when they guy couldnt get an answer from the buzzer (surprise!) and said they would reschedule the appointment for after 7 this evening.

The size of the drop does seem very strange so I am more than happy for the Transco guy to run his own tests when he (hopefully) comes round later on this evening. There is no smell of gas though.