Confused about problem refilling a CH system.

[WaterTight]

Drained down a 8 rad system with a combi upstairs in shower room and - apart from 1 small rad in same room - rest are downstairs. However I was told before starting that 1 never works at all because they think it was disconnected and one always struggles to get warm.

I was draining to add a rad couple metres along from one in kitchen.

Pipework routes are a bit of a mystery as house is very big but most rooms don't have any rads/CH at all and are rented out as flats with elec heaters. The rads served by combi are spread throughout the ground floor and all feeds disappear into walls.

Given this (and the fact a few of them didn't drain at all when I drained from one point near where I was adding a rad) I presume there are hidden drops and maybe some other weird routes. The house has been extended and extended repeatedly.

On refilling the flow and return to boiler upstairs got red hot, 3 rads downstairs got red hot but on 2 others (the new one i added and the one it was tee'd off from) got hot flows to rads but returns barely tepid. One further rad in a bedroom had a less hot - but 'getting there' flow and same problem with cold return.

So thought air or blockage on part of a return route shared by a few rads, although it was hard to work out why rads nowhere near each other were suffering but ones in between were fine but as I said, hard to know what routes were going on with pipework.

Did a bit of mucking about with turning off valves to working rads and waiting (no joy) and then drained off some water from troubled rads while re-filling trying to jig it about but no success. Left them to leave it running for a day to see if it sorts itself out but I'm guessing it won't.

So presuming I'm going back, what should I do? I was thinking drain down and refill again and if no joy I could maybe fill system from bottom up with a hose on a drain off?

As you can probably tell I don't do many jobs like this so not many tricks of the trade do I have...

Thanks for any tips.

 

[tolly]

Probably needs balancing by the sounds of it.

 

[tolly]

Reverse filling shouldnt be needed on a sealed system. Turn off all the rads bar one (one of the cold ones). Do this to all the problematic rads until you get heat to them, then start balancing it.

If youve already tried this, what was the water quality like when you drained down?

 

[WaterTight]

It was very clear.

The reason I thought it was not balancing is 2 of the 3 problem rads had red hot feeds and cold returns.

But that's just an educated guess. Pushing at my skill boundaries on this one.

 

[Riley]

Stuck TRVs?

 

[Best]

I have had plenty of systems give me problems after I refilled them after draining to do work.
I honestly can't say that I have a specific method of attempting to check for possible airlocks or other faults. I just do the usual - check TRVs pins aren't stuck, balance rads, bleed air anywhere, turn pump speed up temporary, turn any working rads off and close balancing valve. If all else fails, I would open each rad valve on a rad that's not working, into a hose (while keeping the filling loop open slightly if a sealed system). Some systems just strangely airlock, often due to poor pipework runs.
Getting the flow pipe roasting hot to a radiator, doesn't really mean much. The flow or the return pipe can be air locked or nearly blocked and just a slight movement of water will have the pipe hot.

 

[WaterTight]

Thanks for the advice. This is why I only drain combis as I thought it would reduce chances of this a lot. But had a couple probs like this on combi's with drops or weird runs recently. Might have stick to flats or one beds!

 

[Last Plumber]

Is the pump in the combi big enough?

You said it's a large house and it sounds like it has long runs.

 

[WaterTight]

Hmm, not sure.

Will be going back in next couple of days to see if I can't resolve it. Will report back.

 

[WaterTight]

Hmm, not sure.

Will be going back in next couple of days to see if I can't resolve it. Will report back.