New boiler undergassed. Blame gas meter governor?

[ernie mendoza]

I have just had a new Worcester-Bosch 24i system boiler installed in the loft to replace a 30-year-old non-condensing boiler in the kitchen. Tests show it is "undergassed". The installer says it may be a problem with the gas meter governor, in which case they say Transco would have to fix it. However the 22mm pipe required by the boiler is connected to a 15mm pipe from the gas meter. Should the installer fit a larger pipe to the gas meter instead of blaming the governor and shifting the problem to Transco? Any advice most welcome.

[John]

I'm about to have a similar change with a 30CDi - into the loft. Pipe sizes cannot be readily checked so I may have the same problems and will need an external 22mm up to the loft.

Worcester will give good advice if you know the pressure at the boiler. I had this:

"The recommended working gas pressure at the appliance is 18.0mbar however the boiler will function correctly when set as low as 16.5mbar. In most cases when testing the working gas pressure with other devices in the property this 22mm pipe diameter is necessary. Should your installer be able to achieve at least 16.5mbar on 15mm pipe-work then the manufacturers warranty should remain unaffected. "

[John Rumm]

Easy enough to check. Just work out if the pipework you have is adequate for the required flow rate.

Look in your boiler manual[1] for the maximum gas flow rate required by the boiler in cubic metres per hour. Then use the pressure drop tables shown here:

see if your pipework is adequate can deliver the required flow.

[1] Available here if you have not got it:

[fred]

In addition, if the installer is suggesting that the meter regulator is faulty then invite him to measure the pressure at the meter outlet test point with the o/p present and show that it is out of spec (20mbar

+/-1mbar) with the boiler running flat out. O/P may need to watch out for smoke & mirrors at this point to avoid being duped by a dodgy measurement technique.

Finger in the air suggests it should be 22mm to within 20cm of the boiler but nothing beats the full design process above.

Good info here

under:

3 Working on Gas Pipework a) What size pipes should be used for gas?

[cynic]

Instead of simply blaming the governeor he should fit his manometer to the test nipple on the meter and measure the pressure at the meter with the appliances running. Unles you live in a bugalow with the meter close below the boiler I would say the pipe is likely to require uprating. Transco will probably tell you the same thing

[ransley]

What did the old boiler consume, the new unit is smaller and uses less gas, right. Was a Manometer used to test flow

[js.b1]

If the installers has fitted 15mm pipe from the gas meter, they have fitted too small a pipe. Which begs the question, is the person Gas Safe or sub-contracted from one who is?

[timothypackwood]

As a GasSafe engineer. I would not leave any appliance attached to any gas pipe if the input pressure did not meet that specified in the Manufacturers Installation Instructions. If there was a problem with the meter governor, I would ask the O/P to attend.

[No Name]

As I understand it, a competent GasSafe engineer should be doing calculations on the pressure drop along the gas pipework taking into account its length, diameter and gas "load for each appliance connected.

The idea is that when everything is running at full pelt, the prssure at

*any* point in the pipework is still +/- 1 mBar of 20 mBar

Where gas pressure is insufficient, the practical solution is to actually increase the pipe diameter accordingly to bring the pressure drop to within 1 mBar.

In my case, I have 28 mm pipe from the gas meter, This runs to the landing floor where it then Tees off to two off 22mm pipe.

One feeds a 38 kW COmbi boiler and the other then feeds the cooker which comprises of two gas ovens and a 5 ring hob. (one of the burners is a Wok burner)

So expecting a combi boiler to run off at least 10m of 15 mm copper pipe is unrealistic. Either uprate the pipe diameter or fit a smaller boiler and then complain how the hot water is not hot enough or has poor flow rate!

[Chris Hogg]

I imagine Mr Mendoza has either had it fixed or blown himself to smithereens in the intervening ten years...

[Fredxx]

While you are correct, it is welcome to have someone this group who is both versed in gas and helpful. Elsewhere these two characteristics seem mutually exclusive.

[John Rumm]

Yup helpful is good, but I would kind of hope one quality you can count on in a gas fitter is attention to detail :-)

And yes, for the OP, his 24kW boiler will have a gas rate of around 2.2 m^3/hour [1]. And a 15mm pipe will not be able to supply that gas rate through 15mm pipe over an effective pipe length of much over 4m [2], which makes it unlikely that it would be ins spec at the time of fitting.

[1]

[2]

[Cynic]

This thread was resurrected from 2010. What's gone on this time?

[Tim+]

I suspect other web portals are copying Home Owners Hub and are presenting old messages as new. Can?t be arsed to check though. ;-)

Tim Packwood, maybe you could enlighten us?

Tim

[Brian Gaff (Sofa)]

Well back in 2010, I imagine its probably blown up by now anyway. Brian