15 or 22mm pipes for loft boiler

[jackohelp]

I have recently changed my rads. boiler is in the loft (converted to bedroom, so also has a rad). I took out some lengths of 22mm pipe on the first floor and replaced with 15mm.(it was a mess and noisy so decided to replace it while changing to new double finned rads) I cant seem to get all the rads hot particularly the two furthest away on the ground floor. If i shut all rads off the two furthest get nice and hot. as i try and gradually crack open the lockshields on the rest the two furthest cool off.
Set up as follows:
loft- 1 rad and trv
1st floor - 3 bedroom rads with trv's and 1 bathroom towel without trv
ground - 4 rads without trv's
boiler worcester 35cdi
digistat on coldest part i.e- landing first floor

Downstairs takes ages to warm if at all. upstairs TRV's set only to 2 or 3 (not max)
Should i put the 22mm pipe back in across the first floor to increase flow or is the pump not up to it. I understand you can get in line pumps. Advice please!!

 

[chrishutt]

You may need to reinstate the 22mm pipes, depending on the total load being carried. roughly speaking 15mm pipes will carry up to 6 kW with an 11 C temperature drop. A greater load will result in a greater temp. differential.

My guess is that the problem is a bit more complicated. There might be air or sludge inhibiting the circulation. You may need to get a competent heating engineer in to assess the problem.