Repairing an electric bathroom heater

[Daniel Prince]

My electric bathroom heater has stopped working. It is a NuTone model 920 heater. It was made in 1957. It fits into a metal can in the ceiling which is just under 13 inches in diameter. It is rated as 1,000 watts at 115 volts.

My brother looked and he cannot find any electric heaters that size. It has a fan in addition to the electric element. It also has a thermal fuse which is open. The thermal fuse says on it:

BOSS WX|

The last character on the second line looks like a vertical line but it might be the numeral "1" (one).

I connected it to power for a several seconds. The fan runs at full speed and the heating element heats up.

I have looked at thermal fuses on eBay. I did not see one that looks like the one I have. The ones I found had several different temperature ratings.

Does anyone know what temperature rating I would need? Thank you in advance for all replies.

[Bob(but not THAT Bob)]

These guys know - they list the 920 heater parts:

[Colbyt]

Just spend the $50 or so to buy a new unit. That one has served the household very well. At least that is the route I took with a 1978 model.

[Daniel Prince]

How do I modify my ceiling to fit the new heater? Do I have to remove the old 13 inch diameter can? Do I have to cut back the drywall until I have a rectangular hole with joists on each side?

[Jon Danniken]

Whatever you do, don't buy it from ebay. Purchase the part from a reputable electronics parts dealer (mouser, digikey).

The problem is that thermal fuses don't set themselves off for no reason. Besides replacing the thermal fuse, you will have to fix whatever problem caused it to open up in the first place.

Often times, and especially on something that old, the bearings in the little shaded pole motor that runs the fan will dry out, or just plain old go bad, and they aren't replaceable. Some of these motors will have a provision for lubrication, however, and sometimes lubricating them will get them going for a little while again. The point is that even if it is spinning, it may not be spinning up to speed, and that can cause overheating (resulting in a thrermal trip).

Jon

[hallerb]

hack repair on this might burn down your home. 1957? thats my age.

replace it newer will be much safer, and assuming its a exhaust fan look for a clogged exhaust

[Robert Green]

Did you contact NuTone Customer Service for assistance at 1-888-336-3948? They may be able to suggest something . . .

-- Bobby G.

[Colbyt]

The metal can is most likely just the junction box for the heater.

All of these that I have ever seen are surface mounted units. Yours may have a recessed junction box as mentioned above. You should have drywall under what you remove.

Here is a link to picture of one:

Finding one that is the same size or larger would equal no drywall repair.

Colbyt

[hallerb]

Thermal fuses fatigue fail; after awhile. If you knew the blow temperature you copuld replace it with a similiar one of the same blow temp.

Its also possible the fan ouput was low fr any reason. a blocked exhaust or failing motor. some motors slow when they start to go bad.

also possible is a bad thermostat that allows the heater to get too hot over time.

line voltage has likely increased over the elderly fans life.

years ago 110 volt was the norm today its about 125 volts.

higher voltage increase the output of the heater elements.

ME? I would replace the heater, its had a very long life...

Incidently I fix machines for a living that use all sorts of heaters. I am akinda expert on thermal fuses, heaters etc

[hrhofmann]

If it started working, you do NOT have a thermal fuse, you have a thermal circuit breaker that opened and then reclosed after some physical jostling. You should check the fan spins easily and that the duct work is not clogged. A slow fan or clogged ductwork will cause over heating and tripping of the thermal circuit breaker.

[Daniel Prince]

It is NOT surface mounted. I removed the old heater. Most of the heater was inside the round metal can which is just under 13 inches in diameter and about 7.75 inches deep. The bottom of the can is flush with the ceiling drywall. With the heater removed, there is a big, deep, hole in the ceiling. The hole is the size of a large cake or a hatbox.

[Daniel Prince]

It started working after I bypassed the thermal fuse. The thermal fuse is a strip of copper that should be bent over a ceramic arch. The copper strip is riveted on each side. One side is broken or melted. The copper strip is now straight and no longer bent so it does not make contact with the terminal on that side.

[HeyBub]

I wish all I had to worry about was spontaneous human combustion.

[hallerb]

was there a vent line on that fan?

[Sjouke Burry]

one:

>

So you expertise is to replace anything you come across? Big solution. I would run the unit as the OP did,and check around the failed component for the temperature, and estimate what that would be in summer . If that value is reasonable,add ~30 degrees, and buy a fuse for that value. Also check the ventilator. Scrapping anything you come across is..... ah silly.

[aemeijers]

If you can get to the top side in the attic, putting in a modern square one is no big deal. Sweep the insulation back, get the old one out, cut the right-size hole, and mount. I have done it from below, but it is a pain.

[Daniel Prince]

The heating element is mounted inside of a bowl. There are vents leading into the room all around the edge of the bowl (between the edge of the bowl and the edge of the can). The fan is mounted on the top of the bowl. I think it is supposed to draw air in from one side of the circle and exhaust it from the other side. There are no ducts or shrouds around the fan.

[mike]

I have the same problem did you ever find a fix or a replacement for this

[hhironaka]

Have been asked to fix this Nutone again, after been sent a free fan unit alledgedly to provide more cfm to keep heater from burning up.

Tech support reported that the heater element was reengineered in 2017 and is now robust and will last.

Others reported installing a 15 minute timer preventing heater element burn out. It will turn off heater but why turn off the needed heater? Lol.

This unit has had the fan motor replaced with a higher cfm rating and is going through a 4th heater element.

Time to either dump and replace this unit or install a separate thermal switch or a timer.