I am Cold

FOREVER21

Might have missed this but does the rads that fail to heat up have thermostatic controls on them.
I had a similar problem radiator would not heat up despite inlet pipe getting hot, took off thermostatic control and it had stuck , gently hit it with hammer and the pin moved more freely replaced valve problem solved. ( very glad as that was the limit of my DIY skills!)

girlsmum

The priest it is :rotfl:
baffled...today i have bled the life out of the system and pump, adjusted the flow valves, checked the thermostats...well at one point i though i had cracked it as the dining room one was hot and the lounge was warm then the hall started to get warm... i was so pleased an hour later the flipping things were cold again and stayed cold :mad::mad:

so I am going to have to admit defeat and call someone in...

oh well thanks all for your wonderful suggestions,

martinsurrey

When they moved the pipes in the bathroom did they use 15mm plastic pushfit? if they did and moved the flow and return for the downstairs, the new pipes cant get enough heat through them.

15mm pushfit is only 6-8mm when you put the inserts in (which is often used to replace 15mm copper), which is fine for 2/3 rads but a domestic pump just cant push the water through fast enough to feed more than a few rads.

I'm speaking from experience. I replaced pipes, had this issue, hot in the rads closed on the run to the boiler, and luke warm tops of rads far away, replaced with copper again, problem solved.

http://www.diydata.com/planning/ch_design/sizing_pipes.php
is a guide on what I am talking about.

http://www.diynot.com/forums/viewtopic.php?t=157180
again more info.

I found it hard to get a good answer as to what BTU you can expect through pushfit pipes.