In an effort to improve comfort and reduce running costs, a couple of years back I obtained a set of Tuya Zigbee Smart Thermostatic Radiator Valves (TRVs). On the whole they weren’t really a very good buy, but they’ve been working well enough that I don’t feel the need to switch them out for something else.
After putting in a freshly charged set of batteries last autumn, they worked away regulating the temperature just fine until spring came this year. Once the heating went off, I forgot about them and the batteries ran out at some point. So they’ve been just resting for the best part of a year!
That would be fine, but being cheaply built throughout, they of course have a healthy serving of cheap grease on the inside. And sitting still is not great for cheap grease, and it’s done what it normally does, turn sticky and gum up the mechanism.
So when I came to put in fresh batteries this year for the start of the heating season, I was greeted with a wonderful big error E1 on the screen and no activity. Of course, I wasn’t going to put up with that and just buy new ones, so I set about trying to fix them. Listening to the TRVs, instead of their normal whirring for about 30 seconds to calibrate the mechanism, there were just two short clicks.
So the cause was obvious - the mechanism has got stuck, and the stiction is causing high current on the motor. The firmware on the smart thermostat looks at that, and thinks - right, I’m at the end of the travel, let’s go back the other way. And it does! But the sticky grease hasn’t gone away so it gets high current when it tries to reverse and just locks up and spits out an error.
The actual fix is simple - just free the motor up, redo the calibration and all will go back to normal. The first step is to disassemble the TRV and expose the motor:
- Remove the outer case.
- Remove the batteries.
- Unclip the display plastic from the top of the TRV (this might differ for some other models?). On mine, there are some sticky conductive pads between the PCB stack and the plastic, but just pulling was enough to separate these.
- Unscrew and pull out the PCB stack from the TRV body.
Once you’ve exposed the motor, you could try to free it up mechanically, but I think it’s easier to do it electrically, assuming you have the equipment.
So the next step is to get a bench power supply set to 3 V (current limit doesn’t matter too much, you’re not going to break the motor with a few seconds at that voltage), or I suppose two batteries in series would work just as well if you had a battery holder to hand.
Then just apply the 3V to the motor terminals, or the motor JST connector on the PCB stack (no need to unplug, you can use the terminals on the back of the PCB as contacts) for a few seconds. Reverse the polarity, and another few seconds. You should hear the motor spinning and see the actuator pin moving in and out (or vice versa).
Then assembly is the reverse of disassembly, and recalibration should proceed without the E1 error.
Let me know if this has helped you!
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