Whale 8l water heater overheating on electrics

I just noticed that there is a small leak (hence the calcium deposits) at the top of the heating element, just above the normally closed overheat cut-off switch.  I can maybe figure out if the switch is behaving. I'm surprised this wasn't picked up by the service, but perhaps they don't check...  

Some further details in case useful to anybody else who treads this path.

 1. The “M5” thermistor read ~2.5 kohms after tripping, when tank is hot and 12.9 kohms when cooled overnight (6 degrees ambient). Seems reasonable but don’t know calibration. 

2. The thermodisc on the electric heating element casing goes open circuit before triggering the overheat condition on the control panel (actually my DVM continuity test sounder warbles when going OC and tripping, maybe because switch is fluctuating between on/off...?)

So either:

1. PCB is broken

2. Thermistor is working but underestimating temp.  

3. Thermodisc is triggering too soon (seems unlikely water gets v. hot)  

I’m considering sourcing a new PCB. They are made by pektron (0178ay2). Seems the malaga Mk4 from propex is the same unit. My 0178ay2 is a 2015 model, so i’m struggling to source an identical version. Whale appears to call it an ak1264, but some purchases are trade only. 

ps. that should have read "0718ay2"

I've only just found this post. Sounds like a similar problem to mine perhaps - also a Whale 8 litre (model WH0802B) in a 2018 model Elddis Xplore 304.

I took mine to a supposed Whale registered service centre for a warranty repair, where they thought it was probably the thermistor fault - but when they contacted Whale, Whale wouldn't assist or agree to a warranty repair because the service engineer hadn't been on a training course for that particular model. Of course I got charged for the experience myself.. and I haven't been able to find another service centre able/willing to do the work that is anywhere near to us.

I haven't myself  tried using gas heating though - just using electric at all times.  I'd have thought that the thermistor was functional regardless of what the source of heating was?

Can I ask what your eventual resolution was, if you did indeed get this fixed in the end ? Thanks.

Maybe you have a calcium buildup problem internally on both heater element and probe affecting heat transfer.

Dear CurrentlyStatic,

I fixed this by fooling the PCB to think it was seeing a higher temperature from the thermostat, thus turning off the heating element earlier and preventing the thermal cut-out from triggering.  I ensured the water temperature was still sufficiently hot by measuring the water temp. at the tap.  In my case it would trip when rapidly heating the water electric+gas.

The thermistor that controls the temperature i.e. tells the PCB when to turn off the heating element is situated top right of the PCB, with black heat shrinked cables.  The thermistor screws into the metal housing.

The thermistors resistance changes with temperature - you thus can add a parallel or series resistance to increase or decrease the effective resistance/temperature that the PCB sees. 

The thermal cut-out (circled in yellow, with orange cables connected it) raises the fault code when it trips, comes built in to the heating element housing - 240 V is across this, be careful!    I believe there is a separate cut-out for the gas, but not the one that was tripping in my case.  

I could provide more details of exactly how I did it, but I'm cautious, because unless you are confident about what you are doing messing around with this is dangerous.  Your changes and fiddling could get you killed (scalded, legionnaired, electrocuted, exploded, lose your warranty !). 

BTW, I went down the calc. route, cleaned the tank with an appropriate acid, and even replaced the heating element which came with a new cutout thermistor, so this was not the problem - it still tripped.  The problem in my opinion is the set point of the PCB or chosen thermistor, which doesn't work when on the fastest heating setting I think the temperature overshoots.  Lastly, you can buy a replacement thermistor, but I knew mine worked, cause I could monitor the resistor/temperature change and it was sensible.  

Pretty annoying that this doesn't work and it appears it is not just my unit that has the problem!  

As an aside regarding my original post - I should have known that there was a small leak from the tank,  cause the whale pump was clicking periodically through the night when no water was being used.  A good tip, if you hear that you've got a problem somewhere with your water system!

Would you know the part no. for the thermistor I have checked the element which works fine but would prefer replacing the thermister the number shown is 36# XE21, but the # is unclear.

I would like to replace thermister whilst i have element out just had to order new PCB ouch !