When I was wiring the boiler, I checked the condensate overflow system on the boiler and noticed the plastic drain was full of black gunk. I cleaned it out and about a week later checked it again and it was dirty again. I looked up dirty condensate and the cause could be that the boiler’s heat exchanger was dirty.
Cleaning the heat exchanger is a maintenance item for the Challenger Boiler. I remember in class, the instructor had installed a Challenger in his daughter’s house as a test. A year later he performed the maintenance and found the heat exchanger clogged with something white. I was thinking calcification from water which of course I mentioned and was embarrassed when he pointed out it was the heat exchanger for hot air, not water.
To open the exchanger, the cover comes off the boiler and the wiring clips to the blower are removed. The plastic exhaust pipe is removed although the pan can be left in. The gas is turned off and the upper gas connection is opened. There is a gasket and washer in this pipe that I removed and needed to reassemble twice because I forgot to reinstall it the first time.
Disconnected Blower Wiring and Gas Pipe
There are several star headed bolts holding on the cover. At first I left the star key on the ring and used a wrench for leverage. Some of the bolts were rather tight.
Loosening the bolts
I found calcification similar to the teacher’s example when ours was opened. But nothing like the black smudgy dirt that was in the condensate.
Calcified Heat Exchanger
I scraped the white stuff and vacuumed the chamber but there was no dirt between the plates. Not all the calcification came off, and I used some emory paper on the cover side too. I could have scraped off the ignitor, shown in the upper right of the photo but I was reluctant to do much because it looked fine and I didn’t want to break anything.
Additional maintenance that I did not do would be to disassemble the blower and clean it and take off some clips on the insulated cover of the exchanger to clean underneath it. But the type of clips were likely to break when I removed them and I didn’t have replacements and the clean look of the exchanger made me decide to wait until spring for more maintenance. Another recommendation is to run fresh water through the heating pipes and vinegar water through the hot water pipes. I didn’t want to introduce a lot of new water into the system having to bleed it again, and the installation of the boiler never mentions having an in and out port for cleaning the hot water side! So I will have to figure out how to port into the supply just before the circulation pump and then on the other side of the boiler to a bucket of vinegar water in order to do that step.
I put the heat exchanger cover back on. It was nice to have help during the removal and the replacement just to be sure of the grip on the cover and to watch for the gasket that must be in the groove on the perimeter of the cover. During the replacement I took the key out of the holder and used vice grips for leverage. This worked much better because the handle was not in the way of the boiler parts.
Tightening Bolts
Maintenance is supposed to be yearly. I have had the boiler in operation about two years although it was used off and on before that. It is not that difficult to do–at least the heat exchanger step is not difficult. Next time I will be more aggressive and have the right clips for the insulated cover.
In the meantime I will just have to check the condensate holder more often to be sure it is not filling with sludge and the water is fresh. My theory is that the heat exchanger was not the cause of the condensate issue. The condensate forms in the exhaust pipe and drips down into a pan that is connected to the condensate trap. It seems likely that that condensate mixes with the exhaust gases and the black is carbonization from exhaust. I will have to do more research about condensing boilers to understand the process better. Somehow the condensate is used to boost the heat to the boiler making it more efficient.