How to Repair Bosch Hot Water Controller YPRM66XB


YPRM66XB bosch controller repair fixI love my Instantaneous Bosch High Flow Gas 26e Hot Water unit. It gives me and the family endless hot water, when ever we want. Well until the other day when we had no hot water. I thought no problem maybe the pilot light didn’t light or something? So How to Repair Bosch Hot Water Controller?

Well the pilot light didn’t light up, nothing did ! So I powered down the unit and restarted it and checked for hot water and I got some back so great another problem fixed. But it was short-lived and the water went cold again after a few days.

Further Investigations reviled that the Optional Temperature Controlled was fried. It was blinking on and off, the numbers were all scrambled and the buttons didn’t work. Time to pull this baby to pieces and work out whats going on. Because damned if I’m going to pay $150 for a new Bosch Controller YPRM66XB. Im going to repair the Bosch Main Controller myself.


Common Bosh Controller Models

The Following Bosch repair procedure should work for the following Bosch Hot Water Controller Models:

  • YPRM66XB
  • YPRS66XB
  • YPRM62XB

So How to Repair Bosch Hot Water Controller?

First, turn off the power to the Bosch Gas Hot water heater. Very Important to Isolate the electrons. This power switch is usually next to the unit its self, tag it out (Do Not Turn On)

Bosch hot water controller YPRM66XBSecond, remove the outer cover of the Bosch Controller and remove the 2 wires (take note where they go) then take out the 2 screws holding the controller to the wall.

Third, take the controller to your kitchen table and start stripping the unit down to get to the motherboard inside. There should only be a few screws. Once you have the motherboard out have a good look over it to find where it is corroded. Yep that’s what causes these units to fail corrosion.

Forth, Take some methylated spirits on a small paint brush and start dabbing at the corrosion it should come right off. Once its all clean make sure its dry and put it all back together and wire it up. Your controller should now be working.


How to Repair the Push Buttons on a Bosh Hot Water Controller

The second problem I had was my increase temperature button on the Bosch Controller YPRM66XB didn’t work. I could decrease temperature fine but not increase. So the unit came off the wall again to diagnose this new problem. To simulate the button, I used a multi-meter on the button set to OHMS and pressed the button. No change in resistance to something on the button was faulty. Repair Bosch Hot Water ControllerNow these buttons are tiny so you can solder new ones on. In the short turn, I used a small cable to touch these 2 points shown on the Picture top left (2x pen lines) to activate to button press while it was powered on. I don’t recommend this as you could touch something else and fry your board. It just got my temp up so the family was happy before my new switch arrives.

Why did my Bosh Controllers fail?

Well due to the location of my controller in the Laundry it is subject to moisture in the air due to my clothes dryer. Having an extraction fan or window vend should help with high humidity in a small space. Other people may have Bosch master and slave controllers in bathrooms which may also have high humidity. As moisture gets on the motherboard it will start to corrode and shots out some Low Voltage components. The Mentholated spirits helps remove this corrosion and dries fast without leaving any residue. Try a heat gun on low or hair dryer to get rid of any left over moisture.


Bosch Gas Hot Water Temperature Irregular Hot and Cold

Fluctuating hot water tempAnother Problem I have had and many others, Is the Hot temperature fluctuates when having a shower. My problem only started when I had a water saver shower head installed. So as my Bosch unit is the Bosch Hot Water System High Flow 26e. I put it down to the unit not being able to regulate the low water flow in the water saver shower head. I’m sure there is a minimum flow rate stated some where but if you are having hot and cold showers try taking out the water saver restrictor in your shower head it should fix your problem.

Good luck with your Repair Bosch Hot Water Controller, leave me a comment if this repair procedure has helped you.

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