Odd radiator behaviour.

[wayfarer]

My daughter lives in a small detached house with a gas fired boiler and radiators. The lounge radiator has never been working correctly and hardly gets warm while the others are hot.This week I removed it, took it into the garden and flushed it through with a hosepipe and it took me an hour until the water ran clear and I have never seen so much black sediment in a radiator. I made sure both valves were working before replacing the rad.
Now the rad. gets warm but not hot.
Here are my observations:

The radiator is at the end of the ground floor run.
The pipe up to the TRV gets very hot but beyond the TRV and into the radiator is only warm.
At the other end, the lockshield valve and ongoing pipe is cold.
When the pump stops running, the radiator and pipe up to the TRV go cold very quickly (in minutes) and don't retain any heat at all, as if cold water is entering through the lockshield valve as soon as the pump stops.
This cycle repeats as the heating switches on and off.

All very confusing to me so any advice greatly appreciated.
Thanks, Stuart

 

[the_d_o_t]

You need to get a powerflush carried out....
Cleaning a single radiator out with a hose is pointless..... as soon as you have connected it back onto the system it will just get filled with all the magnitite from the rest of the system.

 

[Best]

The pipes to the radiator also needed flushed and system could need balanced.

 

[the_d_o_t]

The pipes to the radiator also needed flushed and system could need balanced.

Yes as best has said it wouldn’t mater if you went round and did all radiators with just the hose as the pipework will also be restricted by the build up of sludge.
And the pressure from mains water from a hose is only half a job if that.
Correct acidic chemicals need to be run through the system at heat to break down the sludge and only the power from a powerflush machine will move the magnitite along.

 

[wayfarer]

A poweflush it is then (makes sense now). Thanks for the replies.

 

[Best]

Fernox F5 is very good at putting the magnetite into suspension.
Use it to instructions for full max period in system.
I think the garden hose method and thoroughly flushing each removed radiator would be a good first clean to remove 90% of sludge, if a bit laborious.