Replacement radiator furthest from boiler cold

[nohj]

Hello,

Apologies if there's a topic that covers this, I've read through a large number of posts but I'm stuck.

A replaced a radiator with on my microbore heating system with a new one of the same size, and now I can't get the thing to heat up, here's what I've tried;

There are no TRV's involved
Removed / Checked / Cleaned the two valves
Confirmed that there's water flowing to each of pipes, so no blockage in feed or return pipe
I can bleed the rad, at which point it gets warm, but then get's cold as soon as I shut the bleed valve
Found that the pump (Grundfos 18/60) was not doing anything on position 1 & 2, and stuggling on 3 (althought the other rads were heating up) so replaced it with a 15/60 which is happily heating all other rads
It's a new radiator so there shouldn't be any sludge in it
I've turned off all the other radiators and this one still doesn't get hot
The radiator closest to this (this is upstairs at the end of the loop) - which splits off from the feed / return to this radiator and is downstairs - gets hot no problem
I can access the two microbore pipes under the floor that feed the radiator, there are no obvious kinks or other damage


What could it be? - is it simply an air lock, if so how do I get rid of it and why's that downstairs radiator getting hot?

Any suggestions appreciated.

Thanks

John

 

[tryitandsee]

Was the original radiator working before you changed it for the new one.
Why did you have to change it.

 

[nohj]

Thanks for the response, It was working yes, but it was leaking badly so had to be replaced

 

[tryitandsee]

One of the valves may be at fault. You say you took the valves off and cleaned them. So did the water flow (when testing) from the valves or pipe end.

Have you wrapped too much PTFE tape around the rad fitting or crimped the micro bore pipe somewhere when putting rad back on the wall. Don't know if you can over tighten nut/micro bore on valve, causing crimping!

Just thinking of the obvious.

 

[nohj]

That was my thought as well, but there's no excess ptfe (had it all apart this weekend) there are no kinks, and what's strange is that water will come out of the bare pipe ends or the bare valve ends, and water will come out of the bleed valve, so it feels like a pressure restriction in the rad, but it's new...it has been on the wall for 6 months but it wasn't turned on....

 

[tryitandsee]

Sounds like the water flow has /is taking the easiest route to your rad downstairs. With the fact that it has been turned off, I should think crud or air lock has perhaps collected at either the return or flow where it meets the connection to the downstairs one. Can you gently persuade it to flow with some sort of back pressure, ie with a hose pipe.

 

[nohj]

Its a pressurised system, so how about if I connect a hose to the drain stop (downstairs) as an outlet, and then open the value which refils the pressure from the mains? Would that work or am I likely to rip the thing apart? Thanks for taking the time to answer these

 

[tryitandsee]

Sounds like a plan, perhaps shutting all other rads down that aren't in the equation.

Saves dragging the iced up, dirty hose pipe up the stair carpet, shouting to the other half to give it more pressure!

 

[tryitandsee]

Having now said all that, Im not to sure how a pressure system feeds the rads.
Another may help here!

 

[tryitandsee]

As no others have cut in, I would try your suggestion; if the re-pressure cold fill can circulate around the CH flow pipe, allowing water to escape through the drain off (via hose to outside of course) downstairs.

Personally, I think I would introduce a mains hose to the offending rad flow or return, with the escape as described above. that way you will be reversing the blockage/air lock.

Got to be worth a try.

 

[dextrous]

Close all rads except one. Disconnect new rad. Attach hose to one valve and drape though window

Untitled

• dextrous
• 22 Dec 2009
• 1

Open valve
Turn on filling loop and run to expel air.
Repeat with other valve.