I’ve flushed heater cores several times and had pretty decent luck
It didn’t cause the old heater cores to rupture, the heat output was good and they were still going strong several years later
On a 23-year old Accord, I think it’s worth it to try CAREFULLY flushing the heater core, versus immediately going for heater core replacement
It also depends on the condition of the car and how many more years of service it’s expected to provide . . .
A car-repair experienced diy’er would probably be able to flush the heater core in their driveway on most cars. There’s no seasonal restriction as long as the ambient temp is well above freezing. If the ambient temp dips below freezing when the heater core is full of water from the flush, that could easily ruin the heater core. If you aren’t an experienced car-repair diy’er, suggest to hire this job out, irrespective of the season.
If you are curious how the heater core is flushed, u-tube probably has some vdos, google “reverse flush heater core”.
I’ve flushed heater cores on 3-4 equinoxes after I’ve done headgaskets. Goes from lousy heat to very hot.
I think the major problem is stated above. I would suggest having a mechanic do any work. and as stated by others I would do the head unit first to see if that fixes the problem being it needs to be replaced anyway.
Replacing some are fairly easy but others very expensive. My old cars took less than an hour. My Buick took several hours. Some cars it’s a full day in the shop. No idea about this one but consider the cost in the equation.
If your 2000 Accord is similar to my 1999 Civic, the coolant flow to the heater core is controlled by a valve located near the firewall. The coolant hose from the engine block goes to this valve. As someone moves the heater control from Cold to Hot and back, you can see a wire cable move an arm on this valve, opening and closing it. This works with the engine running.
It’s one reason I bought my Civic. I didn’t want a car with coolant permanently flowing to the heater core because I don’t like the radiant heat near my right foot.
Can a do-it-yourself car owner reach the heater hoses? Do you see them?
As chigurh asked, can you see me?
I see the firewall.
A “where’s Waldo?” of the car world.
I need more brain percentages…
Hand waving. I see them, I see them. That’s similar to mine so I had a mechanic do it.
Is it absolutely necessary for an experienced diy’er to be able to see the heater core hose connections from that angle?
George, the OP stated he knows nothing about cars. That likely includes how a heater core works, and how the control head works. He is far from an "experienced DIYer and is like to cause more damage than he is to fix this thing. The quote of $800 he has for the mechanic to fix this is cheap money and he ought to do it.
No dispute, concur that OP should hire the job out, but it appeared @Nevada_545 was referring to my post above that an experienced diy’er would probably be able to reverse flush the heater core on many car designs. My point is that whether or not the heater core connections are visible from that angle isn’t the critical factor.
It helps when the heater hoses are accessible. The OP probably won’t be able to remove the spring clamps with a common pliers, I have a variety of spring clamp tools.
Heater hoses usually adhere to the heater core pipes, he needs to be able to reach the hoses with his hands and a hose removal tool to peel the hoses from the pipes.