Need to flush heated core 2000 Honda Accord

So I have been having issues so I got my heating, AC, and other control panel issues diagnosed and the mechanic said remove and replace the control head and flush the heated core.

I talked to another guy who’s a mechanic and he suggested I could flush the heated core on my own but since it’s winter I need to do it in my garage and have a hose in my garage. Is this true? The problem is I don’t have a hose or anything like that in my garage. If I could just do it outside with my garden hose that’d great. If it helps, I live in Illinois.

have a hose in my garage. Is this true? The problem is I don’t have a hose or anything like that in my garage.

Witch is either you have a hose or you don’t ?

I’m sorry for wording this confusingly. I have a garden hose that’s outdoors but it’s not in the garage. He made it sound like it needed to be inside of the garage because it’s too cold in the winter.

So the guy verified you have a blockage in your heater core? Sure you can run a garden hose through but can’t guarantee that will unblock it. By the time you figure out what you need to connect the hose to it you might just have a shop do it. Then they can tell you if you need a new one or not and pick you up off the floor when they give you the estimate.

Big difference in temps this time of year in southern or northern Illinois.

Are we to assume that the “issues” you’ve been having is not enough heat in the car? Presumably the shop checked your coolant level and your actual coolant temperatures (to rule out, for example, a bad thermostat).

You can flush out your heater core outdoors with your garden hose. It’s not going to just freeze up on contact or anything. Can you get it flushed out that way? Who knows?

Yeah I explained in detail in my other post (I don’t expect people to go back and see it or anything) but yes no heat and the other controls on the controls panel doesn’t work doesn’t even light up.

He said I need to flush out the heater core and replace the control head.

This is what the mechanic wrote

I’m back (for a minute) after a long hiatus from this site, so have no idea about a prior post. It’s best to just keep with your original thread so people can get the “story so far.”

You need a different shop. To tell you to replace your control head and flush your core sounds a lot to me like guessing. A good shop will simply find the problem (a bad control head OR a clogged heater core). And if your heater core is clogged, they’ll also tell you to be worried about the rest of your cooling system. (Which is also your heating system - cooling the engine makes heat for the cab).

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So I can’t just flush the heated core and replace the control head? I have to worry about that other stuff too to fix the issue?

The first thing recommended on the diagnostic report is to replace the control head.

They must have found a problem with it.

So, flushing the heater core won’t matter. Because if the control head isn’t working, how would you know if flushing the heater core worked?

Replace the control head.



Well when on the phone the guy acted like it would be almost $800 and he was gonna do both so I thought I would have to do both since I don’t wanna pay him to do that. So are you saying I just need to replace the head and see if that works?


And I would get one from out of car at either a U-Pull-It yard, or a local auto recycler.


Flushing the heater core may improve the heat output but since the control panel is inoperative, you won’t know if it helped. An inoperative control panel must be replaced or repaired; this should be done first.

Can you flush the heater core without damaging the hoses and breaking the heater core? If you don’t know about ice, I wonder about your capabilities.

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Yeah sounds like I’ll replace the head first and see if that fixed it. Also, I know pretty nothing about cars so you are correct to question my abilities.

It will be more expensive, but I would replace the heater core, and preferably have a shop do it. I mean replace instead of trying to flush it.

On a 20+ year old car, it’s not surprising that the heater core would be clogged or going bad. If you’re going to go to the trouble to access the HC to “flush” it, you might as well just replace it.

And let a shop do this job 1, because you may not know how to do it and actually make the problem worse, and 2, used fluids are messy to deal with properly. The shop will know how to do everything, or should.

If you can reach heater core inlet/outlet at firewall easily, flushing it could be quite easy.


If I were in your situation, I’d authorize replacement of the control head and then ask for a retest of the heater system. Maybe you can forego the heater core flush. Note that the mechanic said to soak and flush with chemicals not just water. This is to remove corrosion and dirt. If you do this how will you dispose of the chemicals? Flushing into the storm sewer or down the drain in your garage is almost certainly illegal. Where will you dispose of the chemicals and rinse water that won’t damage your environment?

Feel the inlet and outlet houses on firewall. Are they both hot? Heatercore is fine. It’s a 2000 Honda. Has a lawnmower engine. Easy

Well, since the mechanic unhooked the control and forced the output to HEAT, then you should be able to tell if a flush is successful at getting the temps up over 93 at the vent.

Seemed like the mechanic did a good job trying to verify the reason for the low temp. From my own experience, flushing has never resolved a plugged up heater core for me. Even reverse flushing but I didn’t want to risk pushing the pressure amount in case it ruptured the core and made a big mess.

Normally, I just bite the bullet and replace it. But if someone else’s money, I would at least try the least invasive and expensive solution first and get it flushed.

Then as mentioned, look for a used control head…