Boiler Gas Pressure Question

22 Apr 2012
Reaction score
United Kingdom
Hi All,

I would appreciate your thoughts, comments and advice on the below situation.

I moved into a new house a year ago. The house has a few gas appliances:
  1. A Worcester Greenstar Conventional 40CDI boiler that supplies 11 to 15 radiators, and hot water. Although hot water is to a cylinder (not on demand) as the water is also topped up with solar heating.

  2. A gas fire (not used).

  3. Five gas hobs on the cooker (the oven itself is electric).
Looking at the available paperwork, the boiler was installed by British Gas in late 2008 and annual servicing has been conducted by British Gas. The paperwork for the last two years sign the system off as OK, but there is no record of pressure test readings at the boiler.

As a new owner for the house, this year I got a local Gas Safe registered company to conduct the service, and during the service the engineer noted a few things:
  1. The boiler had previously had a fire at some point in time (which had been fixed). This was evidenced by discolouration inside the casing. These issues are apparently not too uncommon with the Worcester.

  2. The boiler needs new electrodes (the current ones have some splits in them) – to be done.

  3. The boiler needs a new automatic event (the current on is on its way out, as evidence by it emitting scale) – to be done.
The real kicker came when he measured the system pressure. The pressure at the gas meter was 20mbar and the pressure at the boiler was 16mbar. Apparently this pressure loss is not acceptable and a 1mbar pressure loss between the boiler and the meter is the ideal, not the 4mbar that was measured!

So to rule out supply issues, Transco were called. Transco arrived within two hours and agreed to replace the regulator on the gas meter to rule it out as the problem. The regulator was replaced, and the pressure at the meter was now 21/22mbar. Transco also looked into their records and stated that the regulator was previously replaced in April 2013 when the supply was increased to 32mm, as a result of a previous “low pressure” callout. With the new regulator in place, the pressure at the boiler was now measured at 18mbar. So still a 3 to 4mbar drop!

So what does my system look like?

Well the gas meter is at the back of the house and is feed by a 32mm supply. This supply splits in to:
  1. a small bore pipe (15mm??) than runs for about 1.5m into the back of the Gas Fire.

  2. a 28mm pipe that runs up away from the meter and passes through the house (at ceiling level, not underfloor) to the boiler at the front of the house. The pipe work between the meter and the boiler is around 6 to 7m in length and appears to be 28mm until the last say 50cm before the boiler, where to drops down to 22mm to enter the boiler. Between the gas meter and the boiler there are maybe 2 x 90 degree bends in the pipe.

  3. At the boiler there is another split in the pipe, with a 22mm pipe running along the from the of house to re-enter the house at the kitchen to feed to cooker. This pipe is around 5m long and has a few bends in it.
So all in all a lot of pipework, but nothing really small (except for the gas fire). So why the pressure loss?

The Service Engineer checked the pipework and filter for obvious issues and suggested that British Gas who installed the system were unlikely to have tested the pressure at the boiler when it was installed and Transco confirmed that British Gas do not tend to do this. So the advice was to go back to British Gas and complain. However given the amount of time that has elapsed this does not look likely to succeed. The Service Engineer also seemed a bit surprised by the pressure loss, given that the pipework between the Gas meter and the boiler was mostly 28mm!

So what are your thoughts? And what would you do?

Is this an issue that I can live with or is it something that can be dangerous? I appreciate that when demand exceeds supply that sometimes appliances can flame out! But in reality my usage is boiler versus cooker. Not boiler, versus cooker, on-demand hot water & the gas fire).

Any advice is gratefully received!

Sponsored Links
Look forward to Christmas as I'm sure others have more to worry about..
:rolleyes: , you get different pressure results depending where you measure from
Last edited:
Sponsored Links
Wow what an assay , I got bored after paragraph 2 then decided to give up , hope you find what your looking for
All joking apart I really don't think you've anything to worry about and as the boys said pressure varies dependant on were the measurement is taken from. Best wishes Bob

Many thanks for the comments. I won't worry quite so much then.

The Engineer seemed concerned that if I had any future issues with the boiler and went back to Worcester that they would tell me to jog-on because the pressure differential was outside the specifications in their installation manual.

He is seemed to be saying that as a Gas Safe registered Engineer that he would not be allowed to install and sign-off a system with such a pressure differential. But as British Gas self certify, they don't bother checking the gas pressure. So based on those comments, I am not sure if he will be able to provide paperwork showing a successful gas service!

@ 18mbar ,if he's checking pressure in the boiler he is talking boll@cks , if i read your post right , got to admit i got a bit bored :whistle:
Simply, no gas engineer is allowed to sign off NEW work which does not comply with the regulations stating a minimum of 1 mbar loss from meter to the boiler.

We are allowed to service equipment where the pressure loss is higher as long as it is working safely and the working pressure at the boiler inlet exceeds a lower figure.

But a slight technicality, the pressure at the boiler is not that measured at the gas valve inside the boiler but at the inlet valve to the boiler where there should now be a pressure test point fitted.


DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links