Triton T80 Easi-Fit+ Thermostatic 8.5kW electric shower, odd flow control problems

[spleenharvester]

Hi everyone

I have one of these titled units, manufactured 2018 and installed 2023. It has developed a problem of being uncomfortably hot even on the lowest economy setting. We've measured incoming water flow at about 12L/min relatively stable and about 10 degrees celsius so I think we can rule out the incoming water supply. Here's the issue and it is completely reproduceable every time the shower is turned on:

1) Turn the shower from OFF to FULL (5.6kW + 2.8kW elements both energised) with temperature dial on lowest. Flow output builds up to 5L/min, and will drop to 3L/min when dial is moved to max heat and then back up to 5L/min if moved back to min heat (i.e. behaves as expected).

2) Turn the element setting from FULL to ECO (5.6kW element energised) with the temperature dial on lowest. Flow initially starts at 5L/min, but slowly drops over about 1 minute to 3L/min (e.g. behaves as if you've moved the temperature dial to maximum). After this point it gets uncomfortably hot and adjusting the temperature dial makes no difference to the flow rate or temperature.

3) If you turn the shower from FULL or ECO to COLD the same drop to 3L/min is observed.

4) The shower continues to behave this way until you turn it back to FULL with lowest temperature dial, at which point the flow rate increases back to 5L/min and the temperature starts responding to the dial as you would expect.

I've never seen a failure mode documented for this unit where the flow rate is inappropriately decreased but only on the ECO and COLD settings. I have another identical potential donor unit with damaged casing, but that one was described to me as having an issue with temperature cycling cold and hot repeatedly (i.e. one or more parts in there is also faulty) so I am wary of trying to replace parts willy nilly and potentially stripping screw threads etc. Anyone know the best place to start?

Thanks very much

 

[spleenharvester]

Solved it, it was the thermostatic flow control valve. After replacing it with the one from the donor I now have pressure back on COLD and the lower setting of ECO. It was still a bit warm for my other half, who likes a cold-but-not-freezing shower, so I swapped the microswitches for the heating elements around (meaning the 2.8kW element is the only one engaged on ECO, not the 5.6kW element). Perfect now, temperature floor is a lot lower, there's a bit of a gap between ECO->max and FULL->low but we are much happier with it!

 

[spleenharvester]

Spoke too soon unfortunately, fault has returned, something seems to be sticking again. Presuming my donor unit doesn't have a faulty part with an identical problem, the only things I haven't tried are the solenoid and heater can, so will be trying those next.