Any tranny van heater experts out there? A mate of mines heater has packed in working. Put's out a miserly amount of heat on motorway and none at all the rest of the time. Presumeably heater matrix is blocked. Any advice would be much appreciated.

From that description it sounds more like the Heater fan's packed in or a air flap is stuck in a closed/mid position.

Hence when your going faster on the motorway air is forced naturally through the Heater Matrix, I can turn the fan off completely in my Kangoo on the motorway as more than enough air if forced through regardless.

does the fan work? start by digging out leaves from the vents at the front!

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Thermostat?

yeh fan is working. Never thought of leaves though but seems to flow air through vents ok.
We'll check airflap and pipework for leaves first. It's an ex- Telecoms van and actually has a little hot water heater and tank to wash ur hands. Don't know if this complicates it at all, but that doesn't work either.

I would have thought a stuck thermostat would make engine overheat unless it has a separate thermostat for heater. As you can see I know bog all about heating systems and we don't have a tranny van manual.

Fit a new thermostat if the coolant level is OK . That way at least you know the engine is reaching normal operating temperature. Transits don't normally have any bleed points in the system but if the additional heater is connected to the cooling system check. If the heater flaps are directing air through the matrix and it is still blowing cold then the matrix is likely to be blocked. Mr Muscle sink and drain unblocker works well I'm told ( better than most flushing agents)