No heat in 94 XJ6. Thermo is ok as coolant reaches correct temperature. Coolant levels correct. Checked the heater control valve on back cylinder and it is not stuck closed. It operates correctly with a/c closing it too. I operated by hand and with vacuum. Next the hose going to firewall from HCV is hot. However, hose coming out of firewall back to water pump is cold. Per Haynes manual ran a hose of water into line in firewall to check if heater core was impeded or blocked. It is not. Ran hose of water through lines at HCV and water flows nicely through. So if coolant going to heater core inside car is hot, and blowers work, then why is return line cold? Both lines should always be hot if HCV is open which it is.

 

What you did makes sense to me.

Have you tried running it up unpressurised (cap off) to chase an air-lock?

Your water pump is working??

 

+1 possibly air or a blockage in the return line?

 

Thanks for suggestions. Was thinking water pump or air void too. Because I took one line off at firewall and flushed with garden hose and appears to be no blockage in heater core or any lines as water flows. Will try running unpressurized. Does seem that maybe water pump is not circulating well enough as not much pressure felt on top or bottom radiator hoses.

 

Don't forget to keep us updated, hopefully it will work for you

 

Isn't there a small electric assister pump on the heater hot supply ? If this fails it can act as an obstruction, rather than an assistance