Central Heating, cold rads only downstairs?

[plumb_boy]

Can you help me? I have a gravity fed heating system (10mm pipe) in a small house, the rads are stone cold down stairs but red hot up stairs! I dropped all the water out that would come out via cock on the Glowworm boiler and then filled up again. To find ALL rads would not heat up at all??
The pump seemed to run even with whatever the heating was set to 0 and got fairly warm so I switched it off with fused switch!
I need some ideas fast.....!!

 

[Softus]

You might have gravity fed DHW, but if you have a pump then you have pumped CH.

The usual cause of hot upstairs and cold downstairs is a failed or worn pump.
It could also be a blockage in the feed to downstairs.

When you drained the system, did you inspect the feed and expansion cistern in the loft? I ask this because it's a pretty common occurrence that there is a blockage in the cold feed - this would result in your system being empty of water, hence the pump would run and get very hot but the rads would stay cold; the boiler would also reach temperature very quickly!

Did you vent the rads before turning on the pump? If so, did you get water out of them?

Also, what colour was the water that came out when you drained the system?

 

[plumb_boy]

Thanks for that.
I noted that the cistern in the loft drained fully when the water was removed and filled fully later when turned on.(plastic cistern)
The down stairs rads still had water at the bleed screws (could have been residual) when water was fully dropped out via the boiler?
I tried bleeding off water at the rad valve tails but nothing much came out there either??
The water I bled off the boiler was a little grey but nothing startling. I did detect some heat at the 3 port valve when restarting as well.
Cheers

 

[Softus]

Thanks for that.
I noted that the cistern in the loft drained fully when the water was removed and filled fully later when turned on.(plastic cistern)

That's sort of good, but unless you checked that the fresh water drained out of the cistern when refilling you might still have a blockage.

The down stairs rads still had water at the bleed screws (could have been residual) when water was fully dropped out via the boiler?

This is a worry - to get water out of a rad vent when the system should be empty!

I tried bleeding off water at the rad valve tails but nothing much came out there either??

This is often the case when the vent is closed, and doesn't tell us very much.

The water I bled off the boiler was a little grey but nothing startling. I did detect some heat at the 3 port valve when restarting as well.

I know I'm banging on about sludge and blockages, but microbore (10mm) pipework it is quite prone to this condition.

I would drain the system again, observing what happens to the F&E cistern.

Before that, you may wish to try one trick - connect a hosepipe to a drain cock and the other end to a mains cold tap. Open the DOC, then get someone else to carefully open the cold tap while you watch what happens in the loft. If you don't get a rising water level in the F&E then you have a blockage.

Only when you're absolutely sure that the system is full of water should you turn on the pump - otherwise it could run dry and be damaged.