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GL2000 Mach 3, heater issues

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Hi guys.

I am having a hard time figuring out which relay controls the heater and which relay is the thermostat.

Measuring for AC volt I have 0 volt out from the board to the heater. I have set the controller in a way that heating should start. Controller temp sat to 38’C, water temp is 15’C.

Flow through heater is ok.

I think it must be one of the small relays, but Im not sure. I think its K6 and K7 but cant find any references on internet.

When the spa is on, I measure 12Vdc for the coil on both relays. So in my opinion both relays should be energised and close the contact. Only K7 is closed while K6 is open. When I turn the power of and measure across the contacts, both are open.

Anybody know which relay is which?









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Remove the 2 copper tabs from the heater element and then test for power off the copper tabs if you don't get power with the element disconnected and the heat indicator light is on then I would be removing the circuit board and looking on the backside for burnt or darkened areas around the relays. Relays are replaceable and I recommend replacing all the relays while you have the board out to freshen it up again. Relays are a wear item and inexpensive. It is an older board and they will all have wear. 


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Thanks for the reply but I have already looked over the back of the circuit board with a magnifying glass and a bright light. Did not see any bad soldering points. Have order 5 new relays, so then I have to get more if I need to replace all. I was hoping to get to know where the 2 or 3 relays operating the heater was located.


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It was running fine until the heater acted up.

Have tried to find a new plug to fix the earth connection. Its temporary fixed.

I replaced both temperature sensors because they did not read the same when i put them in a cup of hot water.


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Got feedback from the supplier that K6, K7 and K8 are controlling the heater. The only thing I dont know is which relay is controlled by the thermostat. 
Any of you know this?

Anyhow I can measure which relay is activated when water temp is 15’C and setpoint is 38’C, (relay on) then turn the requested temperature below 15’C. (Relay off)

Regards Bjørn.



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K7 is controlled by the thermostat. 
When the heater should have kicked in, I measured an open contact on K6 and a closed contact on K8. (Coil on K6 had 12Volt)

Soldered a small wire over the contacts on K6 and then the heater functioned properly. This was just a quick fix, I’ll replace all relays when received from China. Ordered them now and they will be delivered in September!? so I hope my quick fix works until then😉 Very looong lead time!


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I suspect he is in the Netherlands.

I can have them from Digikey in a few days but in the US, it's easier. Most on line sources have a minimum quantity of 10, still, at $1.81 each, I would have just bought 10 and been done with it.

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