Baxi Combi's

[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.

 

[Leo21]

So at what point while commissioning a Worcester say, do you decide your gas supplies inadequate? Do you accept a 2.5mbar drop or decide to enlarge feed?
Im not being pedantic, it's just a lot of my jobs are upgrades and boiler swaps.
You go in and you see a 22mm feed and you've not 100% sure of the route. And you think I'll pipe it up and see, it gas rates within mi specs. But your 2.5 mbar down. What then?

 

[AWheating]

fit a test nipple under the boiler, cost about £4 in fittings and your can then prove the pipework is correct. If you are getting a 2.5mb drop through a WB id say for sure the pipework is undersized tbh.

 

[Leo21]

Ok, so why do wb say there is a possibility of a loss through the gas valve and filter? And go on to say this is acceptable.
Excuse me if this is like pulling teeth, but why have the manufacturers brought out this new bulletin if its not valid?

 

[AWheating]

I dont understand the importance of what the manufacturers inlet pressure difference is really in your pipe sizing? It has no bearing on your gas supply design. It does not matter if there is no drop inside the appliance or a 10mb drop inside the boiler, your gas supply design would not be effected only your ability to confirm its suitability without additional test points.

with the TB's what they have done is inform engineers that there is a likely drop on there boilers between 0 and 1.5mb depending on the model (some manufacturers say upto 2.5mb). They have done this just to avoid confusion on our part as to what readings we get from the appliance inlet test point. This means for us engineers you can not rely on this test point to prove that you have the correct gas supply and the manufacturers are giving us the information telling us we cant rely on there test point. One reason for the tech bulletins i would assume is the high number of boilers the manufacturers attend under warranty and Gas Safe have noticed with undersized gas supplies and the number of engineers that in recent years have used these lower figures from the manufacturers as a reason not to correctly design and install the supply.

Gas safe in the WB TB have also stated that the gas supply must be designed correctly and suggests this can be confirmed by the fitting of a test point before the gas isolation valve.


Its not the manufacturers responsibility to enable the installer to confirm the gas supply is correct, tho i think it should be and i think they should be made to include a test point at the iso valve (but thats another argument). So in essence you as the installer are responsible for the gas supply, not the manufacturer and you have to be sure the gas supply is correct. You cant just test at the gas valve inlet test point and assume any drop over 1mb is down to the applance workings.

In my experience a very high percentage of boiler changes requires a new or upgraded gas supply, and i tend to assume if i cant see the gas run and the boilers not near the meter that i will be upgrading the gas. If you replace a boiler and find after testing its undersized then you will of course need to upgrade the supply. in many cases im putting 28mm in as standard. The problem is trying to explian this to your customer before hand so you dont have the discussion 3/4 of the way into a job.

you cant control what other engineers quote for and do, you can only do your job correctly.

why manufacturers cant give specific drops for each model i dont know? maybe its because of design variations? maybe it differs dependant of filter conditions? it would be interesting to know.

 

[Billy Bob Bob]

I dont understand the importance of what the manufacturers inlet pressure difference is really in your pipe sizing? It has no bearing on your gas supply design. It does not matter if there is no drop inside the appliance or a 10mb drop inside the boiler, your gas supply design would not be effected only your ability to confirm its suitability without additional test points.

with the TB's what they have done is inform engineers that there is a likely drop on there boilers between 0 and 1.5mb depending on the model (some manufacturers say upto 2.5mb). They have done this just to avoid confusion on our part as to what readings we get from the appliance inlet test point. This means for us engineers you can not rely on this test point to prove that you have the correct gas supply and the manufacturers are giving us the information telling us we cant rely on there test point. One reason for the tech bulletins i would assume is the high number of boilers the manufacturers attend under warranty and Gas Safe have noticed with undersized gas supplies and the number of engineers that in recent years have used these lower figures from the manufacturers as a reason not to correctly design and install the supply.

Gas safe in the WB TB have also stated that the gas supply must be designed correctly and suggests this can be confirmed by the fitting of a test point before the gas isolation valve.


Its not the manufacturers responsibility to enable the installer to confirm the gas supply is correct, tho i think it should be and i think they should be made to include a test point at the iso valve (but thats another argument). So in essence you as the installer are responsible for the gas supply, not the manufacturer and you have to be sure the gas supply is correct. You cant just test at the gas valve inlet test point and assume any drop over 1mb is down to the applance workings.

In my experience a very high percentage of boiler changes requires a new or upgraded gas supply, and i tend to assume if i cant see the gas run and the boilers not near the meter that i will be upgrading the gas. If you replace a boiler and find after testing its undersized then you will of course need to upgrade the supply. in many cases im putting 28mm in as standard. The problem is trying to explian this to your customer before hand so you dont have the discussion 3/4 of the way into a job.

you cant control what other engineers quote for and do, you can only do your job correctly.

why manufacturers cant give specific drops for each model i dont know? maybe its because of design variations? maybe it differs dependant of filter conditions? it would be interesting to know.

have had to run 35mm in the past

 

[Leo21]

Now this says to me that there is a restriction in the gas valve that causes a 3 mbar drop. How does everyone read it?