Central Heating Pipes

I am about to put down an wood floor and need to sort out the pipes
underneath first.
My problem is that I have a combi boiler with 22mm flow/return pipes.
However, whoever fitted the systemhas basically welded 15mm pipes on.
The result is that the pipe is too narrow to allow hot water to flow
out quickly enough with the result that the boiler is constantly
switching itself off and on. So, my plan is to replace the 'backbone'
of the central heating system with 22mm with 15mm for each spur.
I am about to put a wood floor down in my dining room and need to sort
out the pipes before I do. The problem is that the pipe leaves the
boiler runs under the kitchen floor (where it is embedded in concrete)
before it gets to the dining room. So, I have no access to the pipe
under the kitchen floor unless I take up the floor which I am not
planning on doing just yet.
Would it be ok to attach 22mm pipes to the 15mm pipe where it emerges
from under the kitchen floor and, later on, dig up the kitchen floor
and replace the remaining section of 15mm piping?
Reply to
Whilst far from ideal the 15mm pipes should be workable if you balance the heating system.
Depending on the model of the boiler the short cycling might be unavoidable, and still occur with the 22mm pipes. I'd put more effort into checking that the boiler can and does modulate the burner and balancing the heating.
Reply to
Ed Sirett
quoted text -
So, do you think that the system is workable as is without the need to replace with 22mm?
Reply to
Can't say. However 15mm pipe will carry about 6kW so add up your radiator outputs. If your rads are the correct size for the room but are slow to heat up the room then the 15mm pipework may be the cause or the pump output may be too low. If the rads work well but when hot cause boiler cycling the likely reason is too great a gas rate or no modulation if a feature of the boiler.
There is more work to be done before your question can be answered. As has already been mentioned without modulation or a lower gas rate you will still get the same cycling with 22mm once the rooms are up to tempeature. 22mm pipework from the boiler is certainly desireable but is probably a red herring regarding the symptoms you complain about.
Jim A
Reply to
Jim Alexander
quoted text -
Before contemplating such extensive works I would try to eliminate all the other possibilities first. The 15mm pipes can carry enough heat from the boiler if they have enough flow/return difference and/or the water moves a bit faster than we would like.
Reply to
Ed Sirett

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