So the heater in our xk8 still isn't working, when car is fiully warmed up there is the slightest amount of warm air in the dash but not hot by any means, i suspected the auxiliary water pump, but the hoses going to the heater core are extremely hot, both the inlet and outlet, so it appears water is circulating as it should, is there something else i can check before climbing underneath and pulling the water pump to check it?

You may have to look into the specifics for access, but I would start by confirming if the pump actually runs. Use one of those cheap mechanics stethoscopes with a long reach. I would assume a running pump will produce a telling sound. I also believe the pump has its own fuse. Double check it of course, but you can also remove it to check what the pump sounds like when it is off.

You can also pull the (wood veneer) center dash trim off (should just pull right off). 2 more screws and the vents themselves come off too. You should now be able to force the opening of the center vent with the controls. With a mechanics mirror, you should be able to see the heater core. Maybe with a bit of creativity, you can use a infra-red laser thermometer and get a sense of the temperature.

If you look around, there is a way to get the A/C control system to run its own diagnostic. Codes can be produced that can also point you towards vent actuators, etc.

From what I understand, that auxiliary water pump is somewhat of a bear to replace. It involves dealing with old rubber hoses typically stuck in place, and requires some prep work, too, to get stuff out of the way. I would try and confirm the diagnostics before jumping on to that job.

Best of luck, keep us posted.

The Pump (item 2) is a regular but a sticking Water Valve (item 3) comes a close second:


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Sticking flaps from failed Servo Motors (items 2 & 3) in the Heater Unit are a possibility:


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The test is to find the point in the system where the feed pipes are no longer hot.

Graham

I encountered a similar problem. First while the engine is running and climate control is on push the button to show external temperature. Is the reading you get close to what you think the outside temp is. Next with the engine warm set the temp control on HIGH and then check for heat. If you can get heat on high and the external temp reading is off then the ambient air sensor has gone bad.
I could only get A/C when the system wsn't set to high. My ambient air sensor said external temperature was 132 degrees and was trying hard to keep me cool inside. Unfortunately it was 46 degrees out side and I needed heat.