My 2005 Honda Accord has lukewarm heat. The mechanic has changed the thermostat, water pump, head gasket, and just last week the heater control valve. Was working with new valve, lukewarm heat today.

Did you ever add any stop leak products to your cooling system? If so the heater core could be stopped up. Also feel both hoses going to heater core. Are both hot? Is only one hot?

Thanks Dandy for your quick response. Yes, I think a stop leak product was used at some point. I was told by the mechanic that the system was bled a few times to unclog the heater core. He also mentioned how one of the hose was hot and the other was cold prior to him changing the valve. Do you think the heater core could possibly still be clogged or does it sound like the core needs to be replaced completely?

One hose hot and one cold (with an open valve) is a tell tell sign of a stopped up heater core. I would try back flushing it first. This sometimes will unclog the core. If you can't get a good flow thru the core using a water hose back flush method then the core will need to be replaced.

I talking about removing the hoses from the heater core and only back flushing the core. This way you can see what comes out and how much flow you have going thru the core.

Thank you!