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Discuss 22mm Gas Feed for 35kw boiler - How do I know this is big enough? in the Central Heating Forum area at

Hi folks,

i've just moved into a property last month and begun to take note of things that may need attention.

One of which is the feed to a 35kw system boiler appears to be in 22mm flexible steel pipe (tractpipe, or teslaflex or w/e).
Distance from the meter is only 4m-5m or so, and I assume no bends with it being flexible steel pipe. It converts to 28mm copper for maybe the last meter, with a single 90degree bend on it before hitting the boiler.

Im certainly no gas engineer, but given the size of the boiler i'd have strongly assumed it'd have needed to be 28mm to feed that appropriately.

1) What do you all think?

2) Is there any function I can do on the boiler to confirm its getting an appropriate amount of gas from the meter? (it's a 35k worcester bosch green star 8000 life system boiler as far as I can tell)

thanks so much,

Sounds big enough

Get a gas engineer in to test
Nope sorry
One more Question on this,

The flow temp is set to 68degrees on this one, I notice when I turn the CH off, the flow temp immediately jumps down by maybe 10degrees or so, to 57/58c.... an hour later of the CH turning off... it's at 50c or so.

does that seem right for a system boiler? i guess im most shocked at that immediate 10degree drop.
Last edited:
Yes sounds fine
Thanks, i've noticed another weird thing too. This doesn't seem normal.

If the boiler has been off for maybe 2hrs and the flow temp is at say 50c

When I turn the boiler on, its immediately jumping down from 50c, to 40c...then taking a long time to heat up to 70c

Does that suggest a piping issue? with the boiler being very, very new.
The boiler is just responding by limiting the temperature differential across the heat exchanger. You can check the flow direction by feeling the flow and return feeds beneath the boiler

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