back boiler problems

[mickmate]

My inlaws have just moved and are having problems with their central heating. They have a back boiler, make unknown, from which they should obtain their hot water and heating. At present i can get the gas fire to fire up , no problem, but the rads throughout the whole house will not warm up. They are getting hot water, but this may be being heated by the immersion heater in the cylinder. When i click the timer / programmer to hot water for heating mode the central heating pump starts up. The pump also responds to adjustments on the room thermostat downstairs. ie when i turn the thermostat down the pump switches off. When i turn it back up it turns back on again. On further investigation i found all the rads to be massively air locked. I have bled all the radiators but still no improvement. I have also checked the header tank in the loft, that seems to be all ok as well. I have checked all the valves in and around the cylinder cupboard and they are all open, as are all the rad valves. One thing that may be relevant is that when feeling the pipework either side of the pump it feels cold on the feed side, and very hot on the outlet side. Could one of the gate valve spindles have sheared off of the valve gate so that it appears to be open, when it may be shut. Any suggestions or ideas would be appreciated for when i go back their this weekend.

 

[HenryRoot]

Does the boiler fire up? is the motorised valve working?

 

[mickmate]

Dear Henry, thanks for your reply. I am still a bit confused. Have i wrongly assumed that the gas fire downstairs is part of the back boiler itself. The fire downstairs lights up without any problems, and we seem to be getting plenty of hot water. As silly as it sounds i cannot find a motorised valve in the cylinder cupboard at all. Just a variable speed pump on its own, along with the timer / programmer. How in principle does a back boiler system work, is the hot water heated via an indirect coil inside the hot water cylinder, fed by the back boiler downstairs. Or is it the other way round, where the central heating gets it's heat from a coil inside the tank which in turn is heated by the hot water from the back boiler. Meanwhile i will carry on looking for the motorised valve. Many thanks, Mickmate.