Aqua-Hot burner not shutting off

[Jon Wells]

Last night, our Aqua-Hot would not keep going on diesel.  Today I pulled my burner and cleaned off the photo-electric eye (and surrounds).  When I went to test it, it fired up and was burning cleanly.  After letting it run for a bit, I turned off the diesel switch and turned off the thermostats.  I heard the burner stop burning, however, the burner blower was still going.  About every 3 seconds, it sounded like it would pause slightly and then keep going.  It finally did shut down.  I tried running it again.  I ran one of the zones for a bit, then I turned off the thermostat.  I left the diesel switch on, and the burner kept going well past what I would expect.  I asked my wife to check the hot water, and it was noticeably hotter than normal.  The control panel just showed green for the burner status.  Again, after turning off the diesel switch, it did not want to turn completely off until it went through that pulsing every few seconds, for about 30 seconds. 

Any thoughts as to what I should check next?

Thank you,
Jonathan Wells
2006 Monterey Ventura IV, C9 400HP

[Eric Maclean]

 Jon
There is a normal purge cycle after the burner shuts down to clear any products of combustion or perhaps unburnt fuel from the combustion chamber however this should only take 30 to 60 seconds.

The temperature in the boiler is controlled by four disc type thermostats attached to the boil one controls the diesel burner temperature set point (190 degrees) and the second is a fail safe if the first thermostat fails to shut the boiler down at the set temperature the fail safe will shut down at ( 230 degrees) killing power to the controller .
The other two disc thermostats do the same thing for the electric heating element The electric t stats are set at 198 and 230 degrees.
The system can be run with both electric and diesel turned on the diesel will then only run when the heat demand has pulled the boiler temperature down to below the 190 degree t stat cutin which is somewhere around the 175 degree.
The burner will continue to run untill the 190 degree thermostat is satisfied or the diesel switch is turned off.

It may be time to check the disc thermostats using an invaded thermometer to verify at what temperature they are shutting off
You should be able to get the manual through the coach assist library.

Hope this helps
Eric

[Neal E Weinmann]

The purge cycle of my 100 series Aqua-Hot in our coach of a similar age to the original poster’s coach will run 2-3 minutes. FWIW, the controller is the new style and the purge cycle seems a bit longer than it was with the original controller. Also, turning the switch off will not interrupt the purge cycle. The unit will complete the cycle.

[Jon Wells]

Thank you for the information.  I did not know about the purge cycle.  It has been working fine, which is good since we've been seeing low temperatures in the upper twenties.  Our coach originally had a Hydro-hot.  The previous owner replaced it with the Aqua-hot in 2016.  My wife did some searching on Aqua-Hot purge cycle issues.