Tuesday, January 11, 2011

Hot Water Heater - Trouble-Shooting

Troubleshooting a Atwood Hot Water Heater

Restore air pocket in the tank - see Leaking Pressure Relief Valve.

Won't start or stay on

Check the wire connections
- remove, clean and replace

Check house batteries for low voltage

Ensure you have propane

Check for air in tank

Check the thermal cut-off

See whether its clear plastic sleeve is burned or melted. The thermal cut-off is a small diode-like electronic part encased in a clear plastic sleeve, hanging out in midair a few inches above the burner tube's air slots. It is a safety device to prevent a fire if the main burner malfunctions due to obstructions caused by spiders or mud wasps. These obstructions can cause the main burner flame to burn outside the main burner tube. Another scenario where flames can emerge from the air slots is when propane pressure is low. That could happen if you run out of propane, if you take on a load of propane laced with butane in a warm part of the country and then drive to a cold area where the butane won't vaporize, causing a pressure drop, or if your regulator is faulty. If the flame or the heat from the flame contacts the thermal cut-off, the circuit will open.

If it appears damaged, you can verify that it is the problem by bypassing it with clip leads to see if the HWH will then operate.

Like a fuse, the thermal cut-off is a one-shot device... so if it blows, it must be replaced. The Atwood part number is 93866. Atwood sells a replacement kit which includes two thermal fuses, some plastic sleeving, and a couple of 3/16" crimp-on lugs. A cheaper equivalent is the NTE Electronics #NTE8096 thermal fuse, designed to carry 15A and cut off at 98 degrees Celsius.

On my burnt out thermal cut-off, the male and female 3/16" (.187) connectors were both crimped and soldered to the leads. If you decide to make your own replacements be aware that you need to gently clamp a Vice-Grip or pliers with a rubber band wrapped around the handle to provide a good thermal contact between the connector you are soldering and the cut-off device. This heatsink is important; if you don't do this the heat from the soldering operation will probably melt the pellet inside the device and "blow" it. You should both crimp and solder like Atwood does on their replacement kits. This device is in a hostile environment and if the crimp is not perfect, corrosion can build up inside the connector causing resistance and problems. When you are finished check it for continuity.

Be sure you have resolved the problem that caused the cut-off to do its job, i.e., remove any obstructions and ensure full propane pressure.

If you have recently drained the hot water tank, it may now be full of air. Open a hot water faucet to let the air out and the water in.

Soot on outside of panel cover
Soot coming from the water heater indicates a too-rich propane/air mixture, resulting in unburned hydrocarbons. This can happen at high altitudes as a result of physical clogging of the air inlet tube (usually by insects or webs); or because the air/propane adjustment has slipped due to the vibration and jolts of travel.

You need to adjust the mixture by loosening the screw on the slotted air-intake tube, then moving the tube back and forth until the flame is mostly blue with just a hint of orange at the tip. This photo shows an older, pilot-light-type Atwood heater, but the tube is the same.

Broken Tabs on Circuit Board
You may find that both the upper and lower tabs are broken, and the circuit board may also have a crack in the plastic housing on the back of the unit. The design and material of the tabs that attach the circuit board to the housing wall cause the breakage; the tabs are flimsy plastic, and when the screws are put through the holes in these "ears" and tightened snugly enough to keep the board from wiggling, the backward pressure can snap off the tabs.

Use a quick-drying, clear epoxy to attach the tabs to washers, positioning the tab screw holes over the holes in the washers. Then attach the tabs (with their washer backings) to the circuit board, epoxy the crack in the back of the board housing, let the thing dry overnight, and re-install it. The washers serve as support to keep the tabs vertical so there's no stress on them when they're screwed into the metal water heater compartment.

Low Flow at Hot Water Faucets

- Could be a BIG air bubble in the water heater. With the pump on, open the tank relief valve until water comes out, then close.

- There is a cold water entry line check valve that may be stuck mostly closed. This check valve is to prevent hot water flowing back into the cold water lines, and evidently, mineral deposits can build up it to prevent it from opening all the way. This would give you poor flow at any faucet.
Apparently, this valve can be removed and cleaned, or replaced.

Andy Baird, WxToad, Erik H, Joan Taylor, Ron, Chuck
Revised 18, Nov 2017

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