Hotpoint TCYL 757C 6P dryer not turning on heating elements

Hi, I’m having a strange issue with this dryer. The backstory is that it broke a few months ago (it’s my girlfriend’s, I wasn’t here at the time and due to lockdown etc I haven’t been able to visit until now) so it’s just been sat unused since. I had a look and found that some of the “ribs” of the belt had stripped away from it and become tangled around the motor shaft, which had jammed things up and also damaged the jockey/pulley wheel thing. After fitting a new belt and jockey wheel, I put it all back together, started it up and thought it was all working until a few minutes later it stopped with a F04 error code, and after I turned it off/on again and tried again it stopped again with F08 instead (if I’m remembering the order of things correctly). I was able to find the error codes here along with wiring details etc (it seems to be an “Arcadia Module Condenser Dryer with Heater with 3 separate motor wires”).

So I checked all the thermostats, NTCs and heating elements with a multimeter and found that the one-shot thermostat had tripped (which I suppose makes a lot of sense as the belt didn’t actually snap, it instead jammed the motor up which would have stopped all the fans etc so the heat from the elements would have quickly built up). I replaced that (everything else seemed fine) put it all together again and thought everything would definitely be fine now… but it still wasn’t heating up. It seems to still occasionally stop within a few minutes of starting with either the F04 or F08 code, but that’s quite rare – most of the time now it just carries on running as if everything’s fine, but with no heat at all. At one point it did start to heat after I left the program running for a while (maybe 20 minutes or so), but then didn’t heat anymore after turning it off/on again, and I then couldn’t get it to start working again even after leaving it running again for much longer, so it seemed pretty random.

Testing each part with a multimeter, the cycling and one-shot thermostats both read as a closed circuit, the front and rear NTCs read roughly the values the PDF linked above says they should be, and the heating elements read 46 and 58 ohms (measured at the connector end that plugs into the board, so via the cycling thermostat). I can’t work out whether this last reading is a problem or whether both elements are supposed to have the same resistance – all I could find is one source saying dryer elements in general should normally be between 25 and 50 ohms, and another saying they’re fine as long as there’s any amount of continuity. The elements both seem to be working fine when the dryer actually turns them on anyway. I haven’t directly checked the float switch (I’m not sure how all that section of it works or how to get to it) but the wires from it are reading as open circuit which I believe means the switch isn’t activated so there should be no issue from that.

I’ve since tried various things (and got myself a clamp ammeter so that I could easily check/if when there was actually any power going to the elements). What I’ve found is that I can consistently make it work by turning off mains power, disconnecting connector J16 from the board (which is the heating elements, cycling thermostat and one-shot thermostat), powering it back on, starting a program (at which point I know it is trying to turn on the elements as I can hear those relays clicking, which doesn’t happen when it’s in the state where there’s no heat), pausing the program and turning off the mains again (it still remembers that there was in a program was in progress, which seems crucial), reconnecting J16, then turning it back on and resuming the program. It then runs perfectly normally from that point, turning both heating elements on and off individually as needed, but after the program ends (or if I switch it to a different one to make it start over) it generally stops heating again (except that yesterday it somehow kept working all day, despite being run through several program cycles and being turned off for a while between some of them, but today it’s back to the previous behaviour again).

I also tried disconnecting the individual parts that are on that connector, but I could only disconnect the one-shot thermostat on its own and the cycling thermostat plus both heating elements together (as they are wired via the cycling thermostat, and then the wires are soldered to the elements so only the thermostats are actually unpluggable). Somehow neither of these tests had the same effect (or at least not as consistently) as disconnecting the connector which disconnects all of these at once. I am also a bit confused as to why it appears to try to turn on the heating elements with the whole connector disconnected as that includes the one-shot thermostat (and when that trips it goes open-circuit which would be the same as it being disconnected), but it does appear to correctly not try to turn on the elements when the elements are actually connected but the one-shot thermostat is not.

So I’m thinking either something has gone very weird with the control board, or the element at 58 ohms is somehow an issue which the board is noticing as being out of range and deciding not to turn them on at all. F08 is described as “Heater – Open or closed Circuit” which seems a bit odd to me as surely closed circuit wouldn’t be an issue, unless they mean the resistance is too low (or high in this case), which would imply that it can indeed detect that. But then on the other hand, as I said, since replacing the one-shot thermostat it mostly isn’t stopping with an error at all.

Does anyone have any ideas what this might be at all, or any further tests I could do to narrow it down? My girlfriend doesn’t really want to spend any more money on parts unless we can be sure they’ll actually fix it, and right now I don’t even know whether to try a new set of elements or a new control board, both of which seem pretty expensive.