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Apollo HydroHeat: Heat Exchanger clog?


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Thanks for providing a forum for this heating system.

Our home is about 25+ years old, is "hyper-insulated" and heated by the original Apollo HydroHeat unit that came with the house. Our home builder was Bigelow Builders.

We replaced our heat exchanger coil about 2 years ago...total fiasco (exchanger took 4 weeks to get here, only one company makes it, the original install is screwy & the HVAC company said they'd probably stop servicing these sorts of units because they're so problematic in our Chicago surburb...whatever), but glad it's been working since.

However, a few weeks ago, our "fine" city decided to do some work with a water main across the street. That blew a bunch of sediment through our water system. A couple of weeks ago, I noticed that the return from the heating unit was cooler to to the touch. I ended up venting a bunch of hot water from a valve above the cold water supply tube above our water heater. That seemed to clear out any blockages and we were fine with heating from there.

Unfortunately, we just returned back from a week's vacation and I've noticed that the return line is colder again. I tried flushing the system multiple times this morning, but the return line keeps cooling off.

Any tips on what I can do to diagnose/fix this?


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I ended up turning our heater blower off for about an hour during my DIY searching for a fix. For whatever reason, when I checked the return pipe one more time, it was hot again!

So, I turned the heater blower back on and monitored the return pipe over the next hour or so and it stayed hot.

Not sure what happened there...but, I'll take it!

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