Fahrenheat FUH54 (5000w) troubleshooting

[Brian W Evans]

I have a Fahrenheat FUH54 (5000w) heater in my shop and it has worked well for over a year. Now, it cycles on and off every minute or so, even at the highest setting. It used to stay on for hours at a stretch on the high setting.

After doing some research, it seems that the two most likely culprits are the hi-limit switch and the thermostat. I'm not opposed to replacing both but I'm wondering if there is a way to figure out which one (or neither one) is the problem. I'm also open to other ideas.

Thanks.

[Ron Selzer]

1-monitor the leaving air temperature from the heater to see how high it actually is
2- open up the housing and make sure no mice, birds, or rats nests blocking air flow
IF good air flow from the start and not too high temperature then
3- jump around the thermostat so the heater should run continuously
4-replace the high limit, DO NOT RUN WITH HIGH LIMIT BYPASSED OR REMOVED
good luck
Ron

[Jim Becker]

The inexpensive/simple thermostat "went" in my Fahrenheat unit toward the middle of the second year using it. It started doing what you describe and then literally "fried" one day. (fortunately, I was in the shop when it happened and killed the circuit immediately) I ended up replacing the internal part that was a crispy-critter with an external interface and simple wall mount thermostat which was much more reliable, albeit at a cost. (I don't use this unit now because I installed a mini-split, but keep it in reserve "just in case")

[Brian W Evans]

Thank you both.

Ron, I will give your procedure a try.

[Don Jarvie]

The heater will also cycle if the temp is below 50. See page 50 of the manual. I also did what Jim did and installed a new thermostat on the wall. The wire to the thermostat is undersized and could burn up so running the thermostat with 10g solved the issue.

This is cycling is a PIA since I don’t leave to on. If it’s cold out it takes a while to get to 50. If it would stay on then it would be great. It does it’s job but could better.

[Myk Rian]

Since I am replacing the Tstat on my Dayton G73 5kw heater, I think my question is in line.

I have a Dimplex TD522w stat. Double pole. 2 red-black sets of wires.
One of the wire sets is connected to a heater in the stat. The other set to the switch.
The heater runs on 240v @ up to 20 amps. I have one element disconnected for 17 amp draw. Tstat is rated for 22a.

The schematic below mentions connecting the internal heater in-line with the stat and the Dayton.
Do I need to connect the tstat heater, or just use the switch wires? I'm leaning toward just using the switch contacts.

https://www.baseboardheaterstore.com/assets/images/PDFFiles/dimplex_tstd_manual.pdf