Baxi Combi's

[Leo21]

Ok but we're still talking about a 2.5 mbar drop being acceptable through the boiler. Yes?

 

[Mike Jackson]

2.5 mbar through the boiler on the 40Kw. It varies on the boiler output. I had big arguments with a warmfont inspector over this a few years ago. Had a 35Kw boiler with a fairly long gas run but 28mm within 100mm of the inlet. Had a drop of about 2 mbar between the meter and the inlet test point (this was before they put the test point on the gas cock). The inspector was insisting that the pipework was undersized and that we needed to upgrade it to 35mm for some of the run despite calculations howing that the drop over the pipework was less than 1/2 mbar. There had been issues with this before and the company had rolled over and upgraded the gas pipe. I refused to do this and instead cut a test point just before the boiler. Testing at this showed that I was right and really ticked off the company as they had spent thousands upgrading gas runs previously, probably unnecessary in 50% of the cases.

 

[Leo21]

So why does the loss occur if its not because of the induction method? Gas cock to gas valve is virtually the same as a se boiler.

 

[hammers4spanner]

I am a member of the works scheme and its the worst scheme i have been involved in the back up is utterly shocking nearly as bad asthe ga i installed last year 2 pcb's and a gas valve have gone !!!

i have fitted a few he's and have had no call backs as yet but the heat team back up is probably the worst i have come across in the heating industry as yet

 

[hammers4spanner]

Also as a fit perspective they have a utterl carp jig !!!

 

[Linkyplumb]

i have fitted a few he's and have had no call backs as yet but the heat team back up is probably the worst i have come across in the heating industry as yet

Not dealt with Ferrolli then?

 

[hammers4spanner]

Yep ferrolli is easy to deal with

cust - hi my boilers broken down

me- what boiler do you have?

cust - its a ferrolli

me- you need a new boiler !!

jobs a goodun

 

[AWheating]

So why does the loss occur if its not because of the induction method? Gas cock to gas valve is virtually the same as a se boiler.

TB 115 worcester bosch inlet pressures.

states :the integral appliance isolation valve and boiler pipework could further reduce the OP by upto another 1.5mbar.

and note 7 states : gas safe register would recommend that the only way to ensure that pipework design and inlet operating pressure are accurate is to ensure the pipework design (pipe size) is correct. The correct design may be proven by installing a suitable test point immediatley upstream (before) the appliance inlet gas isolation valve to allow confirmation that pipework design is correct.



TB 129 also mentions pressure losses on isolation valve, pipework and filters can be between 0.5mb and 2.5mb on modern natural gas appliaces.


it is incorrect to choose your boiler based on the min inlet pressure the manufacturer requires, no matter the boiler make and model the installer is responsible to ensure that the supple pipework complys to the current requirements having no more than a 1mb from meter to appliance connection. Many engineers use this "grey area" (and its not really a grey area tbh) as a reason to not upgrade the gas supply when fitting new appliances. Infact its bad workmanship at best and very dangerous at worse.

the hard thing for responsible installers who want to work to the correct standards is you have to compete for the same work.

 

[Billy Bob Bob]

TB 115 worcester bosch inlet pressures.

states :the integral appliance isolation valve and boiler pipework could further reduce the OP by upto another 1.5mbar.

and note 7 states : gas safe register would recommend that the only way to ensure that pipework design and inlet operating pressure are accurate is to ensure the pipework design (pipe size) is correct. The correct design may be proven by installing a suitable test point immediatley upstream (before) the appliance inlet gas isolation valve to allow confirmation that pipework design is correct.



TB 129 also mentions pressure losses on isolation valve, pipework and filters can be between 0.5mb and 2.5mb on modern natural gas appliaces.


it is incorrect to choose your boiler based on the min inlet pressure the manufacturer requires, no matter the boiler make and model the installer is responsible to ensure that the supple pipework complys to the current requirements having no more than a 1mb from meter to appliance connection. Many engineers use this "grey area" (and its not really a grey area tbh) as a reason to not upgrade the gas supply when fitting new appliances. Infact its bad workmanship at best and very dangerous at worse.

the hard thing for responsible installers who want to work to the correct standards is you have to compete for the same work.

well said aw

 

[AWheating]

please ignore the spewling and grammer in my post, lost the edit button again

 

[Leo21]

My point was that Baxi want min 19mbar, when as you say Worcestor are happy for less.
The fact that I fit Vaillant who accept 16mbar means I don't have to upgrade the gas as I would a Baxi. At the end if the day I'm following the MI,s.
And let's be honest if the manufacturers say its ok its safe.
By choosing Vaillant I can be more competitive I can make more money and still adhere to the MI,s
All your comments are noted although I don't agree.

 

[AWheating]

you still must ensure the gas supply meets the regulations and is sized correctly tho, manufacturer's instructions only apply to the appliance not the gas supply to it and in any case manufacturers instructions require you to work to the current regs which is a 1mb drop.

the quicker manufacturers pull there fingers out there arses and put test points on the iso valve the better imo, not that it will probably happen but it would stop this poor excuse for undersized pipework imo.

 

[Leo21]

Fair enough, I always gas rate to within tolerances. Check other appliances have enough gas. So to my mind the the t,s are cossed and the I,s dotted.

From what I've been told by Vaillant it is that it's the negative pressure produced by the fan that causes the deficit, not filters and gas cocks.

Im finding myself fitting 28mm for the first 3 to 6m on most installs now, especially on anything bigger than 24 kw.

My intention is to fit apliances correctly and cost efficiently.

 

[Mike Jackson]

My point was that Baxi want min 19mbar, when as you say Worcestor are happy for less.
The fact that I fit Vaillant who accept 16mbar means I don't have to upgrade the gas as I would a Baxi. At the end if the day I'm following the MI,s.
And let's be honest if the manufacturers say its ok its safe.
By choosing Vaillant I can be more competitive I can make more money and still adhere to the MI,s
All your comments are noted although I don't agree.

In the instructions they still state that the gas supply must comply with BS 6891 though. So if you fit a boiler and have a working of 21 at the meter and 16 at the boiler the chances are the pipework is not to spec as the pressure loss over the gas valve is unlikely to be 4 mbar. In the absence of the figures for losses over the gas valve you need to rely on accurate calculations for the gas pipe sizing.

Not giving these figures means that without cutting a test point in before the inlet means you can't be 100% sure that the pipework is correctly sized.

 

[AWheating]

tbh ive never seen great drops caused by the boilers ive fitted. Ive only seen it as stated by the manufacturer on a vailiant boiler, which supprised me as the gas meter was less than 2 meters from the appliance.

one thing to remember is if you need to put in some 28mm you can put it in anywhere on the run, which can be helpful if the meters in a bad position.

 

[Leo21]

So what your saying is that it can still conform and be less at the gas valve. Asking as you can verify it with a test nipple in the pipework?
If yes that's what I've been saying all along! You can have less at the gas valve and it can still be correct.

 

[AWheating]

yes it still conforms aslong as your able to prove a drop of more than 1mb from the meter to the gas valve is not due to pipework being undersized. So its pointless choosing a boiler that allows a lower pressure as the pipework would have to be then same no matter what appliance is fitted if they are the same input.

 

[Leo21]

How can you be sure of that unless you've fitted all the different boilers and tested at a downstream point?

 

[kay-jay]

one thing to remember is if you need to put in some 28mm you can put it in anywhere on the run, which can be helpful if the meters in a bad position.

i know it was done a lot years ago. its called reservoiring on account of the reservoir like store of gas in the larger bore pipe section.
i wasnt aware it was still an approved method though, im sure i was taught that largest sections had to be from the meter stepping down appropriately on each leg??

 

[Leo21]

The other thing is, if Worcestor are saying that there's a possibility of 2.5mbar drop through filters etc. then do you not think that they've tested more than one boiler to come up with these figures? More like every one does it, how would two identical boilers differ?
This reads to me as "our boilers lose 2.5mbar somewhere and were back tracking and you can now lose 2.5mbar, oh and we're still quoting bs number so and so to cover our backs"
Let's be honest they wouldn't have released this revelation otherwise.

 

[AWheating]

How can you be sure of that unless you've fitted all the different boilers and tested at a downstream point?

I dont understand? when you pipe size you use the appliances input, you cant base your pipe sizing on the allowable drop inside the appliance. So you would have to design and calculate the pipe the same no matter what you fit, so you will have the same size pipe be it a 30kw baxi or a 30kw WB or 30kw vaillant etc...... it will cost you the same to install your pipework, so boiler choice cant save you money on that part of your installation.

 

[AWheating]

The other thing is, if Worcestor are saying that there's a possibility of 2.5mbar drop through filters etc. then do you not think that they've tested more than one boiler to come up with these figures? More like every one does it, how would two identical boilers differ?
This reads to me as "our boilers lose 2.5mbar somewhere and were back tracking and you can now lose 2.5mbar, oh and we're still quoting bs number so and so to cover our backs"
Let's be honest they wouldn't have released this revelation otherwise.

The reason why worcester and others state that the gas pipework must meet the current standards is because they know that some engineers will use the lower pressures as a excuse for leaving in existing undersized pipework on boiler changes etc..... Which can be very dangerous.

If you go on one of the WB training days you will probably be told that they have this discussion with many engineers and they have seen tons of issues with engineers using the lower figures as a get out for correct pipe sizing. If you look at there manuals they explain it well.

 

[AWheating]

i know it was done a lot years ago. its called reservoiring on account of the reservoir like store of gas in the larger bore pipe section.
i wasnt aware it was still an approved method though, im sure i was taught that largest sections had to be from the meter stepping down appropriately on each leg??

never heard that term tbh. I was assuming the run was to one appliance.

 

[mfgs]

Why is it that you can upgrade the gas anywhere along the line and it will increase the gas flow? I know you can, but don't understand the science behind it.

 

[kay-jay]

Why is it that you can upgrade the gas anywhere along the line and it will increase the gas flow? I know you can, but don't understand the science behind it.

like i said it creates a reservoir like store of gas which feeds an appliance that is drawing more than the supply can replenish, ultimately the reservoir will run out but by then the chicken is cooked lol.

i suppose it can facillitate an initial high burn demand allowing the reservoir to replenish and the supply to provide all that is required when the burner modulates down.