Raypak 406 heater continuously cycling

[gatorson]

My Raypak heater has started to continuously cycle once fired up. The time between cycling has been intermittent but usually around 20 seconds. The heater will spark and then show “heating” on the display but then “spark” will reappear for a second and the flame will go out. This process will then continue. My spa is set to 104 and will only reach about 97 because of the frequent cycling. I’ve checked the filter and cleaned and water pressure appears fine. I’ve never needed to adjust the pressure switch since my spa is at the same level as the heater. The heater immediately cycles so I do not believe a high limit temp is being hit otherwise the heater would need to cool before cycling. Any help is greatly appreciated to get my heater back to working properly. Thank you!

 

[kadavis]

If this is a digital model is there any error codes?

 

[ps0303]

You could temporarily disconnect the hi limit and them connect the two wires together with a jumper wire. Then fire the heater. If it stays on and no cycling, then you have a bad hi limit switch. Usually these heaters are pretty good at telling you that you have a bad limit switch. You also should check out the unitherm governor as well.

 

[gatorson]

No error codes appear. I’ve looked thru the diagnostic manual and have not come across any mention of a Unitherm governor, is that the same as a rollout flame cutoff? If so, I have replaced the rollout.

 

[gatorson]

I've looked at the pilot an it seems to be rolling out. Does anyone know if the pilot should be this large?

 

[ps0303]

The unitherm governor is on the intake side of the water manifold. There is a round cap that unscrew to get to it, Make sure pump is off when you do this.

 

[gatorson]

Update: it turned out to be a completely missing unitherm governor (someone before me, I guess, had removed it as some point) - this caused excessive condensation which resulted in dripping on the pilot/burners. It was enough condensation to keep extinguishing the pilot. After installing the new governor, it completely eliminated the condensation problem. I also verified that the automatic bypass was not stuck open and changed the gasket headers while I was at it since they were very brittle. 14 year old heater will live on!