Newer RayPak 2100 cycling on/off

Hello gang,

I have a 6 month old RayPak 2100 natural gas heater that is giving me some problems that I thought were related to my new VS pump but now, pretty sure it is the pressure switch on the heater.
The symptom is that the heater is cycling on and off fairly 5 minute intervals. Could have been that my VS pump was not providing enough pressure in a lower speed config. So I made an adjustment to the pressure switch to accommodate the lower pump speed. Seemed to work for a few minutes but then it continued to cycle.

I shut down the heater, removed the leads from the pressure switch and hooked a meter to the switch spades. The switch shows closed and provides continuity on the meter. I change the pump speed to low and continuity shows open. Makes sense since the pressure is really low now. Change the pump speed back up to about half flow and the continuity closes. Good. Run pump and full speed and continuity remains closed. Good.

Hooking the switch back up to the heater, it fires up as it should but starts cycling again even with the pump at full speed. Hmmm.

Power off to the heater and I take the switch offline again then put a jumper on the wires while the pump is running. Heater back on, shows demand and makes the call for heat and fires. It does not do the cycling any longer with the pressure switch out of the equation. And the meter still shows the switch working properly at current flow.

It seems to point to the pressure switch being bad in a way that is not obvious to the meter since the switch is turning on and off as flow changes. But under load which cannot be that much, the heater cycles.

Any thoughts on other things to look at or is it time to replace the 6th month old pressure switch?




In The Industry
TFP Expert
Jul 6, 2011
You shouldn't have made any changes to the pressure switch. Your issue is with water flow especially if this just started happening after you installed a new vs pump. You need to ramp the speed up on the pump. Put the pump at full speed and see what happens. When vs pumps first came out I had a rash of calls on heaters because people were trying to run the heater with lower pump speeds which is not enough for the heater to work correctly. Now I could be wrong on this but again, if it worked fine before you added the vs pump, then is is the pump and you are not getting enough water flow.
Hi ps0303,

Thanks for the cautionary note.

The VS pump had been running at full speed and the cycling was present. In the owners manual it suggests adjusting the water pressure switch for such instances. It also suggests testing the switch, heater off, with a multimeter. The switch seems to be responding appropriately (closed) to the pump at full speed and at 2/3 speed. I took the pump lower just to see if the switch went to open, which it did. Pump off does the same.

So the water pressure switch testing behavior seems correct when metering and when running the pump at full and 2/3. Seems like it should behave similarly when in back on line with the heater but it is not.