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Q: Heat only works when accelerating

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The heat only works when accelerating had a coolant flush thinking that would help it did not . They did bleed it the right way twice the heat works for about 20 mins then goes back to only when giving gas . I changed out the thermostat for a different reason but the problem was still accruing also had the radiatior changed then had it bleed about 6 months ago now it's cold had it bleed twice and still having the same issue

My car has 129000 miles.
My car has an automatic transmission.

A: Hello. I suspect the heater control valve i...

Hello. I suspect the heater control valve is the culprit here. Most likely only opening partially. By only being partially open, it allows more hot water to circulate when the engine load and RPM are higher, as when you accelerate, but not enough otherwise. Another possibility it that the heater control mechanism (most are electric these days) is not signaling the air blend doors. The circulating air controls which "mix" cool and hot air before it comes out of the vents - resulting in too little hot air coming out of the heater ducts. If you would like to have this taken care of, I recommend having a certified professional from YourMechanic come to your car's location to inspect the heater system and proceed with any needed repairs.

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