Hello Norcon, thanks for your prompt reply, here goes.
System has been working perfectly for 18 years, it links a solid fuel Baxi Burnall with a back boiler and an LPG Apollo Si50 with a fanned flue. The Link Fuel 3000 came made up and has 5 motorised valves and the pump. The valves are Honeywell V4043 and the pump a grunfos selectric. The system was installed with a set of Honeywell controls, programmer, room stat, cylinder stat, and rad valves. It was installed following advice from a Honeywell employee, and has worked perfectly for 18 years.
I first noticed a problem about a month ago, when switched on from cold the gas boiler would fire up, shut down in a few seconds, fire up again, then shut down as before. This would go on for maybe 5-10 minutes, then settle down to normal running. It has never failed completely, but seems to need "warm up" time. As this is going on the programmer, which has lights to indicate what is happening, indicates that the pump stops, the CH motorised valve closes, and the slumber valve opens. This opening and closing of valves has now spread to the DHW valve, and occurs when the gas boiler is turned off and heat is supplied by the solid fuel. It is accompanied by a "click" from the control box as if a switch was operating. I have changed the motor on the CH valve and checked that it is operating, also tried the pump, which seems to be working OK.
Hope someone out there can cast some light. Exselfbuilder
