Central Heating Conundrum - odd goings-on

[terryplumb]

Q1. Yes gurgling ,spluttering etc sounds likr air being expelled with the water.
Q2. Yes flow and return would be hot ,probably not identical temperatures.
Q3. Boiler doesn't need to be on ,but the f&e tank must be adequately replenished or air will be entering the system instead of water ,which rather defeats the object.
So you have established that water is indeed being delivered past the valves from both pipes. And hopefully expelled trapped air ( maybe not if the f&e ran dry )
Now bleed all rads and pump and cylinder coil of air.Then turn off all other rads at their trv. Open both valves on your problem rad fully,put heating on and see which of the two pipes going to problem rad heats first ,that would be the flow. Lets know the result

Edit.... Just read your last post ,after typing the above !!!.

 

[MeldrewsMate]

Good.
Now, when you're sure you won't have to drain any more fluid from the system, add corrosion inhibitor.
Then...read up on balancing the system. There are several articles on this site which explain how to do this.

 

[uptoyou]

hi MeldrewsMate

I had added cleaner to the system at that point.
My other downstairs radiator started heating up normally then (quicker and hotter) - not sure if it was getting the air out of the system or the cleaning fluid that did it though?

I drained the system down again abut three days ago to get rid of the cleaner fluid and added inhibitor - everything back up and running properly again!