Why are my radiators cold at the bottom?

[johnski]

Our newly bought house doesnt have a filter on the combi and most of the radiators (microbore) dont heat up at the bottom which im putting down to sludge and other gunk

i intend to fit a filter (not sure which 1 yet) and run some clearer through it (fernox f3 has been recommended)

i am also tempted to remove the rads and take them outside and run a hose through to see if that removes anything

is there anything else that could be causing the cold at the bottom issue?

oh, probably also related to this, i keep getting a error on the combi, something about the return temp (cant remember if its too high or too low), i can get round this if i gradually increase the rad water temp, start at 50 then turn it up 5 degrees every 5 minutes or so, but if i just start at say 65 the combi shuts off and give me the error, related to the rad issue or impossible to say?

 

[Deleted member 120897]

What Combi boiler is it? Some have a filter on the return, which iirc can give your symptoms too.

 

[TedRichard]

Large radiator (2000mm x 70 mm), probably last in run of 15, only heats up in top half. Have removed radiator and flushed through but no benefit. Supply pipe to radiator very hot, return pipe hardly warm. Altering lock shield valve no effect. Open system, all other radiators working fine. Any suggestions?
Thanks in anticipation.

 

[Ben-gee]

Is there a trv on the flow?
If so the pin could well be stuck, remove the head and wiggle the pin in and out with a pair of pliers - if this frees it off the rad will suddenly become hot, then replace the head.