Matt6567 Posted March 29, 2021 Report Share Posted March 29, 2021 Hi all, I’ve read lots of info on the topic but can’t seem to find the right answer. GL8000 M7 board always reports a heater temp limit at 34.0 to 34.5 degrees, it’s in a older Catalina spa. The flow seems fine through the heater (checked filters etc) and I’ve changed the M7 temp sensors and the heater. I presume the only thing left is the board albeit this was replaced in 2016 so could it go bad after 5 years. Thanks for the help. Quote Link to comment Share on other sites More sharing options...
CanadianSpaTech Posted March 29, 2021 Report Share Posted March 29, 2021 Please post photos of the circuit board and also the schematic on the inside cover so we can see what you are working with. What country are you in? Make sure you are getting 240V to the heater. If it is only getting to 93 F you might only be getting 120V and could have a blown heater relay. Also I would inspect the heater element to see if it is covered in calcium deposit. Let us know results 1 Quote Link to comment Share on other sites More sharing options...
Matt6567 Posted March 29, 2021 Author Report Share Posted March 29, 2021 Thanks for the prompt response I’m based in the UK, we only have 240v through a single phase and can confirm it is getting full voltage. When heating below 34 degrees pump 1 runs on low speed (2 speed no circ) the system draws c13.9 amps which adds up to 3kw for the heater remainder for the pump. There is definitely a temperature point, I strapped the spare temp sensors to the outside of the heater tube and plugged them in to the board in place of those in the inside the tube and they read about 1.3 degrees lower so was able to get the hot tub up to an actual 35.3 before it stated heater temp limit. Given the fault suggests that one of the sensors is seeing 47.8 degrees, this would be virtually impossible on the exterior of the heater tube without a pump fault leading me to believe it is the board at fault. Quote Link to comment Share on other sites More sharing options...
RDspaguy Posted March 30, 2021 Report Share Posted March 30, 2021 Just to verify, it is getting 240v to the heater terminal until it reaches a certain temp then the voltage to the heater turns off? Are there any errors showing on the topside? Does it display an accurate temperature? Is it in standard mode? Does the pump continue to run, and the heat indicator stay on, even after it stops heating? Quote Link to comment Share on other sites More sharing options...
Matt6567 Posted March 30, 2021 Author Report Share Posted March 30, 2021 Yes, the heater is getting 240v. Until the error occurs at 34c it heats for a number of hours at a rate of 1 degree an hour. This is until the ‘Heater Temp Limit’ error occurs which shuts down the spa. This turns off the heater and pump and requires the RCD to be switched off for a period of time to reset. Yes it is in standard mode and the topside panel is displaying an accurate temperature. Although I haven’t been monitoring the temps sensors through the test feature at the time of error yet. Thanks for the help, found the previous invoice for the board and it was replaced in 2018 with no visible signs of damage. Quote Link to comment Share on other sites More sharing options...
Matt6567 Posted March 30, 2021 Author Report Share Posted March 30, 2021 Sorry I forgot to mention that I’ve replaced the temp sensors and the heater. I made sure to align the heater element correctly. The sensors that came out and measured within spec at 19c and 37c. Quote Link to comment Share on other sites More sharing options...
RDspaguy Posted March 30, 2021 Report Share Posted March 30, 2021 8 hours ago, Matt6567 said: The sensors that came out and measured within spec I love it when people say stuff like that. What, exactly, do you believe "specs" to be? I have seen a few hundred ohms difference (small fraction of a degree) cause errors. Your description certainly sounds like a flow issue. Quote Link to comment Share on other sites More sharing options...
Matt6567 Posted March 31, 2021 Author Report Share Posted March 31, 2021 I took the specs from the Balboa M7 technical service manual, link enclosed, page 20. https://www.hottubdiy.co.uk/user/Manuals/Balbo_M7_guide.pdf I appreciate small margins can make a difference hence why I replaced them along with the heater. I have a new 2 speed pump arriving today but am leaning toward an issue with the board. My understanding of test mode is that pressing ‘light’ and ‘temp’ should display the values for both sensors alternately. However my system do not and only shows one sensor value continuously, a reversed ‘b’ which I assume is sensor b. Tried to find a video of it just to check I’m doing it correctly. Quote Link to comment Share on other sites More sharing options...
RDspaguy Posted March 31, 2021 Report Share Posted March 31, 2021 Well, that chart is useless. I look for a difference between sensors less than 200 ohms. I don't care what temp it thinks it is, as long as both sensors match. If they don't I replace both. But, I will say again, your description sounds like a flow issue. Quote Link to comment Share on other sites More sharing options...
Paulw26 Posted January 22, 2022 Report Share Posted January 22, 2022 HiMat 6567 I am wondering how you got on solving your problem as I appear to have the self same issue, my tub stays at 34C despite being set at 38.5. Apart from checking filters and the heater resistance I haven't done any replacement or checks. Quote Link to comment Share on other sites More sharing options...
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