I'm not getting any cabin heat in my 2000 Insight. 3 weeks ago the heat disappeared for 10 minutes during a long drive but then came back on for the rest of the trip. After that the heat disappeared for longer and longer periods until now there's no heat at all. I've replaced the thermostat, done the burp procedure very carefully, checked the valve to the heater core (it works fine) and back flushed the heater core (there was no sign that the core had been clogged). The little motor that opens the valve to the heater core works fine--I can see it moving--and the blower works fine, just no heat. At this point I can't think of anything else I can do short of removing the heater core unit, which obviously I want to avoid since it involves first removing the dash. Am I missing anything? Is there anything else I can try before removing the heater core? Thank you for your time and your suggestions.

I started a thread here with a similar issue recently, reporting no cabin or screen heat for the first 9 miles on a cold day, and then experienced a serious over-heating incident on the next drive. The car is now off the road with a diagnosed head gasket failure and blocked radiator. In my opinion your concern is sensible.

It's been difficult to establish exactly what exactly happened to our 2000 car, but the best ideas from the guys at the Honda garage and the mechanic who recovered the car are:

1. Poor coolant condition allowed partial freezing and head gasket damage, leading to loss of coolant into engine and drop in coolant level, leading to thermostat and cabin/screen heater problems. Radiator also end of life.
2. Blocked radiator in cold weather preventing circulation, leading to thermostat and cabin/screen heater not operating (when cold) followed by localized boiling and head gasket failure (when hot).

So I suggest checking the coolant level/condition. If it is low (and no leaks) then you might have #1. If you get the radiator checked/flushed then you can rule out #2. In our case the heater and water pump are thought to be working fine.

Thanks for the suggestions. I did check the valve where the coolant enters the heater core, and also the coolant and cooling system condition generally. The cooling system was just serviced last summer and new coolant added. It's all in good condition. The cabin heat occasionally comes back for a few minutes--never very warm though--but then disappears again. I thought everything pointed to a blocked heater core, but that wasn't the case. If anyone else has any ideas I'll be grateful for them. Thanks

I just went through this 2 times this year.... both times after a long road trip

First time the thermostat was fubared after 1 year being replaced.

Second time I went from 90 to 70 cuz the gf was to hot, when she said she was cold, I turned it back to 90 and it stayed cold....

After 45 minutes I got it home, started messing around, the valve before the heater core was stuck closed, eve with thermo on 90*. I manually opened the valve( was tough) and i got my heat back instantly.

You could also have air in the heater core still. After I did my thermostate, I drove around a day and lost heat again and car got hot, right after running it hard on the highway. I burped it/ refilled and was fine, just a idea.

I thought everything pointed to a blocked heater core, but that wasn't the case. If anyone else has any ideas I'll be grateful for them. Thanks

Could be a block of air in the coolant system. When the coolant was added likely via the radiator cap at a change, was the air purged from the system?

Since the rad cap's lower than the highest point of the Insight's coolant system, air purging is required after a change; topping up the coolant system afterwards should be accomplished via the overflow container, where the level is checked.

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