NO Heating! PLease help

[onlyjohn]

Hello everyone, and thanks for reading this.
The problem.
I have a central heating system that was working last winter, and I ran it once in the summer and it was ok too, but it doesn't work now.
I have a back boiler type of system.
I have a honeywell st699b programmer,honeywell v4073a mid-position valve, a grundfos pump, radstats but no room stats.
Hot water works fine, but no heating.
I have bled the radiators, removed the pump and the impeller spins lovely, no gunge found.
I had a plummer round to look at it yesterday, he confirmed that the pump is ok and the mid position valve is ok.
He turned up the thermostat on the hot water tank and the whole system started, i.e. hot water and heating.
He was baffled about how the system can work without a room stat.
the upstairs radiators warmed up but not the downstairs. He said that I turn the upstairs radstats off and let the heat circulate to the downstairs rads and the reason that the downstairs ones hadn't warmed up was that the system hadn't been on for a long time. then he left.
I turned off the upstairs radstats and waited. The heating stopped. All rads now cold (me too)
Any suggestions gratefully received. Thankyou.

 

[ChrisR]

It's probably sludge (accumulated rust etc), unless all the downstairs rads are turned (stuck) off. The soulution is probably a Powerflush, costing £300 - 500. It will almost certainly have worn the pump a lot, add another £100 say with valves.