My Ideal Classic FF280 will only stay on for 2 minutes then cuts out.

I have recently been having problems with radiators, which I suspected was sludge, so I switched everything off, drained down the system (Open vented indirect, cylinder on 2 floor, 2 tanks above in attic, boiler in bedroom close by), added the cleanser and topped the system back up. I bled everything, no problems there, I bled the Central Heating pump (Grundfos Selectric 988123), no problems, the boiler (air release valve on top of central heating pipe, no problems and a bleed valve next to the cylinder.

When I started up again, I switched the central heating on but left the boiler off, let it run for an hour, then checked all bleed points again. Once I was sure I had got all the air out I switched the boiler on. I got it to produce a tank of hot water, but the radiators didnt heat up. The motorised valves definitely work, and the central heating pump is working.

So now I have a situation where the boiler is only igniting for 2 minutes. What I have done now is switched the immersion heater on to heat the water, then I was going to switch the central heating back on to see if the pump will push the water to the radiators to prove that there isn't a blockage anywhere.

Thats where I am at now. Any advice appreciated on methods I can use to identify where the problem is at.

Many thanks

Henry, January 2008

you say that your circulating pump is going, but is it pumping water have had same problem and found that impellor was not rotating. when system is switched on feel both flow and return pipes. there should be no great increase of heat as pump should disperse it.

Robert Nelson, November 2009

I had a similar problem and cost me alot of time and cost found at the end it was the check valve to the flow pipe and cost me less than a fiver to replace after draining the system replacing and restarting the boiler and re -bleeding the radiators

RAJ, February 2008

Sounds like you have an air lock. Try isolating all radiators but one. Run the CH boiler and see if it heats up. Repeat with remaining radiators. This should push the airlock into a radiator and then you will be able to vent the air from the bleed screw.
Failing that. Drain down. Isolate the electricity supply to CH system. Open and 'lock' the motorised valves manually with lever on the side(spring return type). Refill the system venting the upstairs rads first. GOOD LUCK

Squires Gas, February 2008