Rad lockshield problem

[matgriff]

Hi, been having problem with my CH system in a house that we've recently moved into. Worcester Bosch 34CDi combi, 12 rads, system is 2yrs old all piped in plastic.

Long story, two rads downstairs dont get hot, one tepid one cold... completely bled all the air out, balanced up the system as best I can, no success

Through a process of rigourous elimination I've isolated the problem. Basically with all other rads shut off, just these two on full with lockshields fully open, the boiler short cycles and the rads still dont warm up, so I reasoned it must be a blockage of some sort. Both lockshields have drain cocks on them.

If I shut the TRV's and open the lockshields fully, then open the drain cock on either rad, the water doesn't gush out at system pressure, it just runs slowly... If I then open the TRV it gushes out fast and plentiful.

If I try this on any other rad with a drain cock on the lockshield, it gushes out if either the TRV or the lockshield are opened.

So the problem is either in the return pipe from the rads to the manifold or the lockshield isn't opening (or is blocked)

Does this sound plausible ??

Thanks

Mat

 

[Madrab]

Yup

 

[John D v2.0]

Yes, or the manifold has a restrictor that's turned down? if it's plastic pipe it shouldn't be so much trouble to disconnect the pipes and blast then out.

 

[matgriff]

Could I try connecting a hose from the mains to the drain cock, opening up another rad drai cock and back flushing the pipes ?

Mat

 

[Madrab]

yup, worth a try, just try and isolate the boiler as well as the other rads as you don't want crud flushed up through that. That being said you really want to avoid using the valves under the boiler to do it.

 

[matgriff]

Hi, the two offending rads are in the same room and both have drain cocks on the lockshields. I planned to back flush up one and open the other, so the water should take the shortest path up, through the flow/return and straight out of the other one .

I guess as long as there's no other path to the outside world then nothing should go back into the boiler or other rads etc ?

Thanks

Mat

 

[Madrab]

Hmmm, that's a fair assumption and it should but couldn't guarantee it

 

[matgriff]

I fixed the problem..... realized as soon as I got the rad removed, the cowboys who'd installed it tried to bend the 10mm pushfit piping back on itself through 90 degrees to get to the lockshield as the pipes natural run were both to the right.... of course it kinked and blocked the flow/return. Just need cut it and add a couple of 90 degree bends and re-make it off.

Thanks for the help

Mat