solid fuel heating

[CXR100]

ive got a call coming up in work to go and fix a solid fuel heating system , log burner runs a gravity indirect hot water cylinder and a pumped open vent heating system run with a hi - lo limit stat to run the pump to circulate the water to the rads. the problem is that the heating wont work. electrician been there, stats all working fine and pump switching on to circulate water, but rads wont get hot, any ideas? thinking airlock at first, presume that id get rid of it like a normal system, close all rads open one by one kind of thing, but the call ive had is that none of them work , so any ideas? don't know if the immersion heater is on constantly yet. could it be something like a blocked cold feed or something, only been plumbing 6 years so far including my apprenticeship and not done a lot on fault finding on open vent systems. any help appreciated. thanks

 

[Best]

Firstly check there is water at all points of the system just incase a feed pipe is blocked. When you take a small amount of water from any part of the system you should see the expansion & feed tank ball valve filling in.
I wonder has anyone being doing any work to the system & caused an airlock? I guess it is possible there is a check valve fitted that is stuck, but unlikely. The pump might appear to be working but is faulty.
Feed pipes tend not to block usually on gravity primaries, unlike pumped.