Hi,

Been having some issues with my heating over the past few months - most of the time only cold air comes through even when the dial is turned to maximum heat. It does occassionally blow warm air to begin with, but this soon turns cold.

I've tried replacing the heater control valve and then tested the new one by turning the ignition on and could easily hear the valve click open.

I've also had the heater matrix out and flushed it - no gunk came out and it seemed to be clear inside.

After putting it all back together I let the engine run idle for a while with the heat turned to maximum (and no blower). Took the cap off the expansion tank to allow any air out of the system and felt the pipes going into the matrix - both were warm (inlet was the hottest). The coolant is topped right up too.

Went to turn on the blower and hot air was coming out, so I turned it down to cold and cold air came out. I then turned it straight back up to hot and almost immediately the air turned cold again.

If it's not the heater control valve and the matrix isn't blocked, what could it be?

Would the thermostat cause symptoms like this?

Any suggestions welcome!

Cheers