Hi all, I have just p/xed my old shape 2.8 ducato motorhome for a 2008 3.0 motorhome. The new one has a fan switch on the dash near the headlight adjuster switches, which controls a fan behind a secondary radiator under the drivers seat to give heat to anyone travelling in the back. The problem is that it blows cold air. I have taken the front cover off the seat and found a bleed valve on the top pipe, but no air came out just water. I let a bit more water out and the pipe got luke warm but then went cold again. Is the problem air or something else? is there any other bleed valves anywhere? should it be bled with the engine running or off? Thanks in advance.

The heater works via the engine coolant so was engine up to temperature and confirmed good heat output from the normal cab heater? The underseat heater plumbing is T'd into the heater flow and return pipes just prior to the cab heater matrix witha sertvo valve in the flow line. When you switch the underseat heater on the fan starts and the servo valve opens allowing water to flow to the it.