New boiler gas supply question

[Mike4]

If the new boiler is going in the same place as the existing one and using the same supply pipe, why can't the pressure be measured at the existing boiler?

Adrian

This is a good point that warrants further comment. You are correct PROVIDED the rate of gas consumption of the proposed new boiler is no higher than the input rating of the existing old boiler. If the new boiler is going to be bigger, i.e. capable of consuming gas faster than the old, the pipe sizing calculation should be carried out.

Most installers don't bother though as the result will usually be 22mm and sometimes 28mm, but as 28mm is so much more expensive, they usually kid themselves they made a mistake and 22mm will be fine. Which it always is as far as whether the boiler actually works, and this is all the customer actually cares about as illustrated by many of the posts in this thread. The non-compliance with the gas regulations will be skirted, worked around and generally ignored, probably for the whole life of the new boiler! One point to beware of though is if the manufacturer is called upon to honour their guarantee, they will sometimes seize on an undersized gas supply to wriggle out of their responsibilities under the guarantee, citing incorrect installation.

If I were still installing boilers I think I would be forced by market conditions and the consumer scepticism expressed in the thread to use undersized gas pipes too, and just take it on the chin and install the odd bigger pipe here and there if/when caught out. It is actually one of the reasons for my decision to drop installation works and concentrate on breakdowns and repairs only, about 15 years ago.

[beseeinyou]

I had this scenario last August / September and posted about it, I remember clearly that Worcester Bosch's guarantee would be invalid if the installation was not done as per their installation instructions, notably a minimum of 22mm pipe and the pressure drop readings being within the regulations. Similar to Mr Foolish my meter and boiler are at completely opposite ends of the house (1997 Bryant Homes) and the proposal at the time was to run a new 22mm pipe under the lounge and hall floors into the hall cupboard then through into the garage which could then get into a small loft area above the boiler, so we moved the furniture etc and rolled back the carpets the day before but it didn't quite work out that way !

When he lifted the first board in the lounge near where the meter is outside we discovered it was actually a floating floor with no cavity so going under the floor was not an option, the alternative was to run the pipe round from the meter to the side of the house and go up beside the chimney breast and enter the main loft, go across that and drop down to the smaller loft area at the garage / utility room so in fact the new pipe did not actually go "through" the house, another thing was that this run of pipe was quite a bit longer than the original proposal so it ended up being 28mm, the guy turned out to be a very good installer and I'm glad I didn't go down the cost saving routes that some quoted.

It isn't broken down in my quote but from memory the cost for the proposed 22mm under the floor added on about £500 and when that was changed to the alternative 28mm run he took another £100.

Beseeinyou

[beseeinyou]

Oh and I meant to say about the original pipe run, upon entering the house the pipe goes straight up the cavity wall to the upper floor bedroom and then it runs under the upper floors over to the utility room, all this is hidden of course, the only sight of it is when it comes through the wall in the small loft area in the utility room and drops to the boiler.

Beseeinyou

[MaraMan]

Thanks Mike4 and beeseeingyou. The explanation is very helpful for my understanding, if not in terms of what decision to make. I do get frustrated by the different levels of understanding/explanation given by qualified installers. I don't know if this comes from their contempt for their customers, or laziness, or incompetance, or greed. I think that at the end of the day I will take the pragmatic approach and let them install an 18Kw boiler, and let them test that it is working properly, keeping everything crossed it won't need a new pipe. As the installers are accredited by the boiler maker and if it subsequently has an invalid guarantee due to inadequate/improper pipework then I guess I will look to them to rectify the problem.
Cheers again
MM

PS - our current gas pipe goes under the floor and it would not be practical to run the new larger pipe the same way.