Thanks for reply ��. Nothing fancy at all. Just a steady and solid 88 88.
No segments no flashing. It’s as strong and solid as you see above.

 

Doesn't sound like you have any codes.

This has to be a clogged heater core or the blend door not diverting the hot air to your vents. You can try removing the heater hoses at the heater core, then run water into the side that is less cool to reverse flow and clean any blockage in there. You will have to look to see if the blend door is opening/closing properly when you switch from cold to hot.

I would think that a bad water pump would cause you to have overheating issues in the engine, but I am not familiar with the diesel setup.

 

heater matrix is clear as a bell. I ran water through without issue. Blend door is my last possible avenue. But all cables and gadgets in the footwell appear fine. And to be honest I’ve no idea how to access this blend door so any direction welcome. I would guess its same for left or right hand drive. The cables and heater mechanisms are in the right side footwell or USA passenger side.

 

Coming in way late and I admit I have not read all of this.

Heater valves can fail. So if you haven't already, check the temps of the hoses before the valve, after the valve and the outlet hose.

Again, sorry for jumping in and not reading all the things that have been done/tested.

 

Thank you for that advice. Yes it does seem logical. Sadly my diy abilities are hampered by owning two left hands and have zero experience of this issue.
If I could see a problem I would be more confident. I think Honda dealership and splash some cash is my next action.
I will update everyone after 😁

 

Well. Good news at last. I finally got warm air in my cabin. I can only conclude my system was airlocked.

I had to brim the expansion tank, Im saying to overflow! Then disconnect the radiator tophose and pour water into it. Bring the engine up to temperature, then bleed off air via a little bleed valve I found in the expansion tank.

I never had to go to such extreme to bleed air from a cooling system before!

So im going to conclude now. I have hot air in the left side of the car and cool in the right. (yes I know about the dual system) Im thinking more bleeding required.

so thanks to all who had input into this saga. Its been cathartic using this site to vent my frustration.

Re error code 88 88 i was getting from the HVAC diagnostic, it has gone. No more errors.

 

Bleed valve in the expansion tank? The cooling system for the diesel must be different from the petrol engine. Is the expansion tank pressurized?

(now I'm just getting curious, don't know if I can actually help)

 

I can’t comment on the petrol version but yes. The normal cap is the usual half turn to remove. But to the right a few centimetres is a black plastic button screw needs a square head tool to remove or a pair of pliers lol. It can be gently unscrewed almost with fingers to release pressure. I should say there really is very little pressure in the system even at full running temperature.

Im still getting good heat in the left vent but cold to the right. Odd or what?

 

Well, we only get the petrol engine here in USA. And the expansion tanks have not been pressurized. The pressure cap is on top of the radiator & has a hose to the bottom of the expansion tank which allows coolant to be sucked back in during cooldown.

The cooling systems have always been sensitive to air pockets & produced some strange behavior if you didn't remove all the air.

Having said that, if the expansion tank is pressurized, that makes me think the cooling system is quite different. Probably still sensitive to air pockets, but needs a very different method of purging the air out.

 

Just a random thought & I don't know if this will make any sense.

Hot on one side & cold on the other side can be a symptom of an air conditioning system with low pressure. And US Hondas run the air conditioning whenever you direct the air to the defrost position blowing on the windshield - even if you think the AC is switched off.

Try setting the AC manually, switching it off, and directing the air to your footwells only. Now is it cold on one side & hot on the other?