AquaHot Controller Board Repairs ELE-PC4-010

[Gerry f]

I have a AHE 100-04S system.  Everything is working properly but the Engine PreHeat (EPPUMP).

It appears that Q18 burnt up and D3 is shorted on the controller board PN ELE-PC4-010

Does anyone have a schematic for the board or know of anyone that can repair these boards? 

I would like to have the part number of D3 if anyone has it.  I have ordered a new Q18 but the diode has no part numbers on it.

I hate to buy a new board if this one can be repaired since the failure seems pretty simple and straight forward.  I have measured the pump operating current and it's about 1 - 1.1 amps.  The Q18 should have been able to handle that current with no problem.  Just a weak part I assume.

Thanks,

Gerry Faulkner

2007 Executive Sandia IV

[Tom Cherry]

You need to read this.  There is a company that a member recommended that repairs AH boards.  They KNOW the boards....and finally had to help the member install some Relays to isolate a problem....we never figured it out....but he had a gremlin somewhere in the system.  When ONE zone's thermostat called for heat, it would BLOW the board.  Not very logical......and we (Frank McElroy) and myself never could sort through all of it.  But, Lexington Engineering kept replacing the board with a rebuilt one.  We THINK that he had a bad pump for that zone.  We LEARNED that the thermostat signals are just contact closures.  They signal each zone to turn ON.  That then sends a signal (from the terminal strips) to the Zone fans....

However, that thermostat signal also activates each pump.  That comes from the BOARD's PCB and NOT as a separate signal.  When this zone was calling for heat, we BELIEVE he had a bad pump that was shorting out the board....based on where the failure was. He sort of shotgunned it.  Lexington sent him a Relay package that actually used NON Control board voltage to turn ON the fans.  They also isolated the Thermostat signal just to make sure there was no transient voltage on the "dry - Non voltage" circuit. He had swapped a pump....then it started.  He had another pump that he installed with the new relays.  Bottom Line... IT WORKED...

But, he had great repore with Lexington Engineering and they were very responsive....

This might help.  I don't know if we have any prints on the actual boards as to how to trouble shoot the PCB.  However, Ivan, in the above thread also has pictures of a board that had a bad joint or issue and he fixed that.

In the first case....the board would blow exactly (looking at it when it was out) in the SAME area...where the potentially defective pump was located....

Hope this helps...  You can do some searches of Aquahot in the topic or files....

[trailmug]

I assume D3 is just connected across the pump leads, and is doing flyback protection for the Q18 driving the pump. I'd grab a rectifier diode with at least 150V of reverse voltage tolerance, but otherwise choose anything that fits, say, a 1N4003RLG.

Edited June 1, 2023 by trailmug

[Gerry f]

On 6/1/2023 at 6:16 AM, trailmug said:

I assume D3 is just connected across the pump leads, and is doing flyback protection for the Q18 driving the pump. I'd grab a rectifier diode with at least 150V of reverse voltage tolerance, but otherwise choose anything that fits, say, a 1N4003RLG.

Yes.  the diode D3 is connected across that pump leads.  Was able to locate a MOSFET to replace the bad Q18 and got a diode from the local tv repair shop.  The Engine Preheat pump now works!  I did observe an interesting fact.  The engine preheat pump will not start unless the Diesel and/or Electric boiler heat is on.

Thanks for the help.

Gerry Faulkner

2007 Executive Sandia IV

[Frank McElroy]

Thanks for posting the solution and using a MOSFET is a good solution.  All I can say is WOW - you found a local TV repair shop still open.  In my younger days in the 60's  I used to repair tube TV's for extra money.  I thought TV repair shops were all gone today.

Thanks for posting the solution and using a MOSFET is a good solution.  All I can say is WOW - you found a local TV repair shop still open.  In my younger days in the 60's  I used to repair tube TV's for extra money.  I thought TV repair shops were all gone today.

[trailmug]

Thanks for the update, my preheat pump quit years ago, replaced the pump with the newer style and it died again. I resorted to block heater to start and letting the engine pump pull the heat in from the boiler (still works pretty well). I'll have to check someday and see if the problem is in fact electrical.