Some cooler radiators

Bendy_House

Clearly, what you've said about the plumbing changes could also have a bearing on this. If more than one rad is being supplied by 15mm pipes, coupled with it being a longer circuit, but it's obviously hard to tell from here :-)
(A 15mm pipe take deliver a lot, so I wouldn't expect this to be an issue on it's own, but if there are other issues, then it might all add up.)

looking_forward

I will check again but couldn't see any real difference with pump running. 
This rad was in the property from new and up until a week or 2 ago was working albeit at imho a less than perfect output - say 60 -65 so % , when all other radiators were shutdown it would get close to hot but never as hot as other radiators (12 rad system)- So I would say that both the radiator in the living room and the dining room have never been perfect. Pump is a Grundfoss  UPS 18-60 on speed 2 or 3 1500 or 2100 rpm . Runs quietly and no reason to suspect , but i still plan a change in the next few months  as it is old. Then after draining and refilling the system this rad did not work at all and the rad in the dining room is at about 30% . I am really puzzled !    

btw all rad pipework is 8 mm.

plumb1_2

Do not put the pump on , take off rad, put a container underneath the flow and return valves and open up one at a time, you should get equal flow through both. If not you have a blockage. And difficult to shift just with the operation of the pump. Especially if 8 mm
Options , repipe in 10mm/15 mm  or powerflush, connecting the machine to the 2 valves or pipes. You need a machine with a flow and reverse option, and make sure the f&e tank is isolated.

looking_forward

plumb1_2 said:

Do not put the pump on , take off rad, put a container underneath the flow and return valves and open up one at a time, you should get equal flow through both. If not you have a blockage. And difficult to shift just with the operation of the pump. Especially if 8 mm
Options , repipe in 10mm/15 mm  or powerflush, connecting the machine to the 2 valves or pipes. You need a machine with a flow and reverse option, and make sure the f&e tank is isolated.

Yes , have decent flow from both pipes and looks pretty equal

Bendy_House

In that case, if opening the return valve - usually the lockshield, but not always - and allowing a steady trickle out, and then turning on the pump does not affect this steady trickle, summat is surely amiss? (Ideally done with most/all other rads shut off).

Do you have visual access to the plumbing - eg can you crawl under the floor?! I wonder if the cooler rads have been plumbed in as if it were a one-pipe system - ie a tee is taken off a 'flow' pipe, feeds the rads, and then rejoins the 'flow' pipe further along?!

All guesswork at the mo', of course.

looking_forward

I will double check the return with the rest of heating to temperature , but don't think from my previous tests this make a noticeable difference.
    The pipes run in the dry lining .There is some access to the system in a hallway cupboard where the 2 manifolds are and some pipework runs through the garage for the extension.. My plan was to drain system and check for clear flow to and from the manifolds from both these rads, I can hopefully check this and also  see if anyone has done anything controversial with the pipework when the 2 new rads were added.  

Bendy_House

Ah, sorry, I'd forgotten they were microbore, so you have manifolds! Er, forget most of what I've said...

Since you have good access to the manifolds, and you are clearly up to the task, that would sound like a good move - ID the F&R pipes to each rad, and then you can remove and test them as required.

plumb1_2

You need to disconnect the return and pull a min of a bucket of water through it, then you can tell if it’s blocked or not, no good just a cup full, and do it with the heating shut down.

Bendy_House

That's a good point - sometimes a pipe can appear to flow ok, but if left for a bit longer it could drop to a trickle as an airlock or constriction makes its presence felt. I've seen this in the past - an initial strong flow, then a significant drop.

Since you have a vented system, LF, then the F&E tank will keep providing a flow, so you can run it as long as you want.

Also, being vented, the likelihood of air locks is greater, so extra-worth allowing it to flow for a good while to be certain it's ok.

When all is done - ie you've sorted the problem - then you add a fresh dose of inhibitor.

Did I mention a filter? Really worth fitting - it'll start to do its job from the off.

looking_forward

Ok , a brief update from yesterday . Checked radiator (the one hat had no heat at all) and after flushing again could not shift any debris and it flows clean and well. So before I reinstalled I made up an adaptor and gave the flow and return both several good blasts of mains water pressure. I then let several decent jugs of water flow back out through them  - the flow was clear from the start , however the return came through very, very black for the first jug and then cleared and flowed clean. I reinstalled the rad and fired up the system and the radiator is now working again at where it was , say 65% ish heat  . I am going to go down the manifold check and clearance route soon and also analyse the piping for issues. I will certainly install a filter shortly anyway. 

Thanks to you all for your valuable contributions and I will be sure to post an update as and when.