Downstairs rads not working

[jimmy_one_ball]

Hi fellas, sorry this is a bit long winded but here goes,
Right, my central heating stopped working and I know nowt about it. The hot water is still fine and a bloke at work suggested it might be the controller. I have a GlowWorm Fuelsaver U.F.B. 50F fanned flued boiler in the kitchen and a Potterton EP2001 electronic programmer next to it so I bypassed the controller and hey presto all the rads were blasting, we just had to switch it on and off manually, which would suggest a new programmer is all that is needed. Two days later the downstairs rads stopped working and the upstairs rads only seemed to warm up when the hot water is heating up. The boiler is firing up fine but after about a minute it goes off then on and off and on all day off and on off and on. There are four neons that light up on the PCB that indicate a healthy system and we had the pipes flushed of silt a couple of years ago. I've bled the rads and also I found a little bleeding nipple near the copper boiler but no air came out, just water. The pump seems to be working on all 3 speeds, its a Grundfos UPS15-50 Selectric. I closed the upstairs rads and opened the downstairs rads but that didn't do anything so I'm going to take the downstairs rads off in the morning (Xmas day!) to flush/refill and hopefully remove any blockages but apart from that I'm stuck. I can't get a plumber till Jan and its freezing! Incidentally, I replaced the little back up battery in the Potterton and the LCD works fine but when I fix it back to the wall it goes blanc. There are thes pins that plug into sockets to make electrical connections but its still bypassed so I don't think that is stopping the rads from working, so any temporary quick fix ideas are very welcome, cheers and Merry Xmas!

[jimmy_one_ball]

Just as an update, cleared a load of black water from the rads (5 downstairs) but to no avail. Then a mate said look for the actuator valve which I found was a little silver box with an electric cable leading into it, located in the airing cupboard near the pump. Anyway it had a little lever on its underside which was pointing towards "Auto" so i just slid it away from auto and the rads started to work again, magic! Gonna get a combi boiler installed in the loft now as i reakon my system is 18 years old. Thans in advance for any replies to this, Merry Xmas