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Topic: AquaHot short cycling (Read 440 times) previous topic - next topic

AquaHot short cycling

In my 99 320 I have a 431/12 that I have done extensive work on. I have found minimal information on "Short cycling". Only one real symptom is: The AH will dip below 190 or so I believe (haven't actually tested the temp), it will run for about a minute, the solenoid will close and the fuel will stop, the blower continues for two minutes. It will restart shortly after because it likely did not reach its max temp of 230. It does not do this all of the time and mostly occurs during the day.

I have tested what seems like EVERYTHING. I have tested the thermostats for continuity with the AH hot and cold and in between cycles. I have tested the CAD cell for resistance. I have tested the fuel pump for pressure and set it to 145. The blower sounds fine as far as speed goes. It does not go up and down like it used to with bad fuel lines. One other symptom that is occurring is an occasional whistle (sounds similar to a whistle from someone using their fingers in their mouth). I have yet to pinpoint where it is coming from and there are no humans in my bay. The bearings were changed, the clutches were replaced, and the whistle doesn't occur when the motor is detached.

What other things may cause premature stoppage of the aqua hot without faulting?


Here is a short video of the sound it makes https://youtube.com/shorts/uNwS9GkZEws?feature=share
1999 U320 WTFE #5586
2014 Subaru Forester 6sp
4000 watts of solar
650 aH @ 24v

Re: AquaHot short cycling

Reply #1 –
Is the diode wire (red) connected to the number 2 pump connection on the back side of the middle relay.  This pump runs all the time the burner is running to stir the coolant tank to produce a uniform temp top to bottom in the tank.

No stir means the top of the tank gets up to temp well before the bottom does.
Rudy Legett
2003 U320 4010 ISM 450 hp
2001 U320 4220 ISM 450 hp
1995 U320 M11 400 hp
1990 Granvilla 300 hp 3208T
Aqua Hot Service Houston and Southeast Texas

Re: AquaHot short cycling

Reply #2 –
Quote from: Rudy –
Is the diode wire (red) connected to the number 2 pump connection on the back side of the middle relay.  This pump runs all the time the burner is running to stir the coolant tank to produce a uniform temp top to bottom in the tank.

No stir means the top of the tank gets up to temp well before the bottom does.

Interesting. Did not know that. It is connected. So, I have replaced my webasto controller and ignitor with Beckett stuff and had initially failed to put the diode into the wiring. Instead, anytime the bathroom or basement called for heat, the burner motor would run. I just went to feel the coolant line going into the bathroom (while the burner was running) and it is very hot, so I assume the pump is running during the burner cycle. It also just short-cycled again. What I may have to do is go into the bay and make sure the pump is running during a cycle. Perhaps at night, pump 2 is running which helps stir the coolant and that is why it isn't short-cycling at night.
1999 U320 WTFE #5586
2014 Subaru Forester 6sp
4000 watts of solar
650 aH @ 24v

Re: AquaHot short cycling

Reply #3 –
It is not a good idea to back feed the motor when the bathroom or basement calls for heat.  Hence the diode wire.

This may only apply to back feeding the Webasto Control Unit and not to the Becket Control unit modification.  But running the burner more than necessary is not the best use of the burner motor.

Congrats on the Becket mod.
Rudy Legett
2003 U320 4010 ISM 450 hp
2001 U320 4220 ISM 450 hp
1995 U320 M11 400 hp
1990 Granvilla 300 hp 3208T
Aqua Hot Service Houston and Southeast Texas
 

Re: AquaHot short cycling

Reply #4 –
Quote from: Rudy –
It is not a good idea to back feed the motor when the bathroom or basement calls for heat.  Hence the diode wire.

This may only apply to back feeding the Webasto Control Unit and not to the Becket Control unit modification.  But running the burner more than necessary is not the best use of the burner motor.

Congrats on the Becket mod.

Understood. The diode is on there now so the motor only runs when the burner calls for it. I did check and the pump is working with the motor on as the pipes running out of it are hot whereas the other two are not. I will reevaluate later as that red wire connector is loose. I adjusted it and is tight now.
1999 U320 WTFE #5586
2014 Subaru Forester 6sp
4000 watts of solar
650 aH @ 24v