Changing from 10mm to 15mm pipes

[Stmc93]

 Hi, looking for some advice.

 

I have 10mm pipe feeding my radiators but its not feeding enough water into them as they don't produce as much heat as they should and have some cold spots. I don't think the pipes are blocked up because I have flushed them out with cleaners and removed and cleaned a couple of the radiators out and still not enough heat. I fitted a new radiator which also doesn't produce enough heat although it is a bigger one than the others.

 

I have 22mm mains pipes coming off the boiler which I'm guessing reduces to 10mm under the floorboards upstairs at some point to feed the radiators. (Boiler is in an upstairs bedroom)

 

My question is, can I cut the 10mm pipe at a point before the radiator and attach a 10/15mm reducer and feed the radiator with 15mm pipe? Would this work or would I have to lift the floorboards and replace all of the 10mm pipe completely for 15mm for it to work?

 

Forgive me if its a stupid question, I've not long moved into my own house and still learning bits and bobs ?. Any help appreciated, cheers.

[Temp]

Check the pump is working correctly and that the system is correctly balanced first.

[Temp]

 

It would also be worth checking the return temperature to the boiler and the condition of any bypass in the system.

Edited August 14, 2020 by Temp

[scottishjohn]

28 minutes ago, Stmc93 said:

My question is, can I cut the 10mm pipe at a point before the radiator and attach a 10/15mm reducer and feed the radiator with 15mm pipe? Would this work or would I have to lift the floorboards and replace all of the 10mm pipe completely for 15mm for it to work?

yep no point in changing it unless you do -the 10mm size is what will determine flow rate

If indeed it is a flow issue due to pipe size. but its probably not -I had micro bore in a house to upstairs rads and they still worked -but the flow regulator on down stairs rads -you have a valve each end of rad -one is usually a thermostatic one -which turns off rad when room is correct temp 

the one on the other end is to balance flow through whole system 

water will go easiest way -so if you got those not set right you will get a mis match in flow rates in the whole system 

most houses the downstairs rad and more closed than upstairs to make the water go up to bedrooms 

you can try closing bottom rad flow valves and opening up bedroom ones as far as they will go and see

when trying to balance system thermo vlaves should be turned as high as they can go -so they don,t start closing while you are fiddling

 ideally you need 2 thermo couples(thermometer on inlet and outlet pipe) on the rad and you want as big a temp drop across inlet to outlet as possible

20c would be perfect --but doubt you will get that -but if temp drop across bottom rads is same as bedroom ones and inlet temps are the same -then you got it as good as it can  

 

 

[Carrerahill]

2 hours ago, Stmc93 said:

 Hi, looking for some advice.

 

I have 10mm pipe feeding my radiators but its not feeding enough water into them as they don't produce as much heat as they should and have some cold spots. I don't think the pipes are blocked up because I have flushed them out with cleaners and removed and cleaned a couple of the radiators out and still not enough heat. I fitted a new radiator which also doesn't produce enough heat although it is a bigger one than the others.

 

I have 22mm mains pipes coming off the boiler which I'm guessing reduces to 10mm under the floorboards upstairs at some point to feed the radiators. (Boiler is in an upstairs bedroom)

 

My question is, can I cut the 10mm pipe at a point before the radiator and attach a 10/15mm reducer and feed the radiator with 15mm pipe? Would this work or would I have to lift the floorboards and replace all of the 10mm pipe completely for 15mm for it to work?

 

Forgive me if its a stupid question, I've not long moved into my own house and still learning bits and bobs ?. Any help appreciated, cheers.

How old are the radiators? Cold spots are probably not flow issues to be honest.

 

Our house, as we bought it, was all plumbed in 22mm primary flow and return lines for ground and first then down to 15mm as things split off and finally 8mm out from manifolds and T 15mm Tee's with 8mm reducers, we have never had an issue and some of the 8mm runs are probably as long as 5/6m. Must say, on the rater occasion we run the boiler the radiators get blinking hot blinking quick!

 

It may be worth analysing your system and doing a schematic then post it here. I have seen some frankly odd odd plumbing, I once saw an entire ground floor circuit of radiators plumbed in series - if the first room got too hot or the stat was off none of the other radiators got hot! 

 

I also once worked in an office where they ran about 20 radiators around the perimeter walls of the open plan office in series. They told me when I started it was broken and didn't work correctly. I explained the issue and we learnt how to balance all the stats to keep some sort of flow going.

 

As for the change in pipe size, if you are going to upgrade to 15mm then you really want to upgrade as much of it as possible. 

[Stmc93]

3 hours ago, scottishjohn said:

 

most houses the downstairs rad and more closed than upstairs to make the water go up to bedrooms 

 

3 hours ago, scottishjohn said:

The boiler is upstairs so should I choke off the upstairs rads a bit to force the water downstairs a bit more

 

[Nickfromwales]

8 hours ago, Carrerahill said:

How old are the radiators? Cold spots are probably not flow issues to be honest.

Bingo.

Not just the rads, but the valves, particularly if they are prehistoric TRV's.