Single cold radiator in downstairs bathroom

Nuggy96

I recently drained my central heating system (closed loop with a combi boiler) as I'd added some sludge remover (Sentinel X400) to the system. I then put water back in, bled all the radiators multiple times and put it back to around 1.3 bar pressure. However, my downstairs radiator in the bathroom is completely cold (cold at bottom and top), when the heating is turned on. Both the lockshield valve and TRV are open to full. All of the other radiators are heating up as expected in the house. This radiator definitely worked before I drained the system.

I closed both the TRV and lockshield valve on the cold radiator and opened the bleed valve till no more water came out, and opened the TRV, water came out the bleed valve, I then closed the TRV and opened the lockshield valve and water came out the bleed valve. So can't be a blockage?

I am completely lost as to why that 1 radiator won't heat up...

Any ideas? Thanks in advance.

ThisIsWeird

Did the clean work? What did the drained water look like? Did you fit a magnetic filter on the system return whilst drained down?
Anyhoo, your tests are good. If you open just one rad valve at a time, and then the bleed screw, and a good strong jet comes out each time, and continues, then - yes - each pipe must be providing a supply to the rad (unless one valve didn't actually close fully).
Was the bleed jet strong? Did you leave it going for a good 10 seconds?
What happens if you close off the other rads, so only this one is actually 'on' and run your CH?
Did you adjust the lockshields on the other rads when you did your 'clean'? If so, did you return them to their original positions?

Nuggy96

ThisIsWeird said:

Did the clean work? What did the drained water look like? Did you fit a magnetic filter on the system return whilst drained down?
Anyhoo, your tests are good. If you open just one rad valve at a time, and then the bleed screw, and a good strong jet comes out each time, and continues, then - yes - each pipe must be providing a supply to the rad (unless one valve didn't actually close fully).
Was the bleed jet strong? Did you leave it going for a good 10 seconds?
What happens if you close off the other rads, so only this one is actually 'on'?
Did you adjust the lockshields on the other rads when you did your 'clean'? If so, did you return them to their original positions?

Not as good as I wanted, I did put some more X400 in and was planning to drain again in a week or so. I did let out a little water from the draindown tonight and the water was quite brown. All the other radiators are working fine though.

There is a magnetic filter on the system.

Yep the bleed jet was strong, and the lockshields haven't changed since before it was working. I am very confused

david29dpo

As above, turn all the rad rads off except the cold one and put the heating on. See if if gets hot.

Nuggy96

david29dpo said:

As above, turn all the rad rads off except the cold one and put the heating on. See if if gets hot.

So turned all rads off at TRV except the cold one. The radiator made loads of sounds and then started heating up! Thanks, unsure what happened there.

I'd say there was a blockage but weird that water still came out of bleed valve with the valves open.

Anywho! Thanks!

ThisIsWeird

Nuggy96 said:

david29dpo said:

As above, turn all the rad rads off except the cold one and put the heating on. See if if gets hot.

So turned all rads off at TRV except the cold one. The radiator made loads of sounds and then started heating up! Thanks, unsure what happened there.

I'd say there was a blockage but weird that water still came out of bleed valve with the valves open.

Anywho! Thanks!

Let's see if it'll still keeps hot once the other rads are reopened!

Yours is a pressurised system, so an air lock would be very unusual, but I guess not impossible. I suspect that if you kept the bleed screw bleeding, it might peter out or slow down - the flow to the rad wasn't 'full'. But only a guess.

Keep checking that Mag filter and see what it collects.

When you drained the system down after the chemical clean, did you open all the bleed screws to allow each rad to fully drain?

Veteransaver

It's probably the trv needle seized, try taking the trv head off and pushing it down gently to see if it frees up (try pushing it down with a flat metal object like the side of a hammer, but don't hammer it!)
The rad will still have filled with water probably from the second pipe (hence why it bleeds ok and is full of water), but obviously it needs to flow across the rad via both flow and return, if either side isn't flowing then radiator will stay very cold

Nuggy96

ThisIsWeird said:

Nuggy96 said:

david29dpo said:

As above, turn all the rad rads off except the cold one and put the heating on. See if if gets hot.

So turned all rads off at TRV except the cold one. The radiator made loads of sounds and then started heating up! Thanks, unsure what happened there.

I'd say there was a blockage but weird that water still came out of bleed valve with the valves open.

Anywho! Thanks!

Let's see if it'll still keeps hot once the other rads are reopened!

Yours is a pressurised system, so an air lock would be very unusual, but I guess not impossible. I suspect that if you kept the bleed screw bleeding, it might peter out or slow down - the flow to the rad wasn't 'full'. But only a guess.

Keep checking that Mag filter and see what it collects.

When you drained the system down after the chemical clean, did you open all the bleed screws to allow each rad to fully drain?

Stayed hot when I opened all the TRVs on the other radiators.

When I last drained I added more Sentinel X400 as I think there's still a lot of sludge in the radiator. This was confirmed when I took some water out of drain down valve yesterday.

I read somewhere last time that when I empty the system to close all radiators and open 1 at a time and use the filling loop under the boiler to flush each radiator once. Does that seem right? I didn't try it last time and secondly by "closing the radiator" will just closing the TRV be enough or should I close the lock shield valve as well? (I'm just being lazy cause the lock shields are quite stiff)

Nuggy96

Veteransaver said:

It's probably the trv needle seized, try taking the trv head off and pushing it down gently to see if it frees up (try pushing it down with a flat metal object like the side of a hammer, but don't hammer it!)
The rad will still have filled with water probably from the second pipe (hence why it bleeds ok and is full of water), but obviously it needs to flow across the rad via both flow and return, if either side isn't flowing then radiator will stay very cold

Not sure if this was the issue as I had the lock shield valve closed and opened the TRV and water came out the bleed valve (post empty) and vice versa. If the lock shield valve is closed and TRV allows flow I don't think it's a seized pin?