How to Repair Bosch Hot Water Controller YPRM66XB

YPRM66XB bosch controller repair fix
How to repair Bosch Hot Water Controller

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 whenever 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 did have some 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 Controller 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)

You are going to need some tools. Every home handyman should have these electrical tools in their garage.

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.

Corrosion in electrical circuits is usually caused by a high humidity environment. Our dryer is close to the Bosch hot water controller.

Forth, Take some methylated spirits on a small paintbrush and start dabbing at the corrosion it should come right off. Once it’s all clean make sure it’s 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 the 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 Controller

Now, 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) drawn on the circuit board.

This is to simulate a 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 temperature 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 it dries fast without leaving any residue. Try a heat gun on a low setting or a hairdryer to get rid of any leftover 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 somewhere in the manual.

If you are having hot and cold showers try taking out the water saver restrictor in your shower head it should fix your problem. At least my family can have hot fun showers again with their color changing shower head.

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

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  1. If the controller has only two wires, is this just a variable resistor system? I need to lower the temp on mine in a standard unit. Bridging options only increase the temp.


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