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Gas pipe supply size question for new boiler

View the thread, titled "Gas pipe supply size question for new boiler" which is posted in Boiler Advice Forum on UK Plumbers Forums.

So we are looking at a new vaillant ecofit pure 418 regular boiler but have a question about the gas pipe size requirements..

At the gas meter the pipe size is 15mm where it then runs under the kitchen floor before exiting at the the other side where the existing boiler is located (old baxi) where the pipe size is 22mm. So somewhere under the kitchen floor it changes from 15mm to 22mm.

The old boiler has been working fine with this configuration but i am worried that new boilers require a 22mm pipe.

The new boiler will either be a Vaillant or another Baxi rated at 18kw as due to the position etc it has to have a rear flue....

One surveyor mentioned the 15mm pipe size may be ok but mentioned new pipework might be required if after the new boiler was fitted the flow rate wasn't sufficient. It will be an absolute nightmare to do this as the existing gas pipe runs under a kitchen floor that was only last year levelled with resin before new lino was stuck over the top....There is no obvious easy way to re-route.

The 15mm gas pipe that exits the meter we estimate runs for around 3-5 metres before the size changes to 22mm somewhere under the kitchen floor. It's probably around another 3metres to the boiler.

I read somewhere that the Vaillant has a 15mm connection, not sure if that matters.
As an after thought does anyone have any opinions on the vaillant ecofit pure 418 or the Baxi 418 Heat 18kW?
 
If the existing Baxi is 18 Kw, it will use the same as the new 18Kw Vaillant (near as damn it). You need to ask a Gas Safe registered installer to test the existing supply pressures so you know how it is currently performing.
 
If the existing Baxi is 18 Kw, it will use the same as the new 18Kw Vaillant (near as damn it). You need to ask a Gas Safe registered installer to test the existing supply pressures so you know how it is currently performing.
Cheers, the existing is a 22 year old 24kw, the new 18kw should be sufficient.
 
Cheers, the existing is a 22 year old 24kw, the new 18kw should be sufficient.
If the existing is sufficient then it will be for a smaller boiler yes.

There will be a pressure drop from meter to appliance and you need to know what that is now in order to know that is is sufficient now. If there is 15mm tube in there - even a short length - then it will cause a noticeable and significant drop.

The best way to 'know' is to test the working pressure at both ends on full rate.
 

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