Replacing the flammable vapor sensor in your hot water heater

Part of the toils of home ownership is the hassle of repairing appliances and fixtures. In the financial freedom world one could rent or even live like a digital nomad. But that doesn’t work if you plan to enroll your kids in traditional schooling or even hold a professional job. The nomadism comes after financial freedom, unfortunately.

This leads us to today’s DIY review. My five-year old hot water heater decided to act up last week and punished the household with cold water. Fortunately with many modern hot water tanks have a gas control kit installed. This control unit helps maintain the pilot light and allows you to adjust the temperature of the water.  In layperson’s terms, this device keeps the water hot, whether through natural gas or electricity.

The beauty of these controls is that they also provide error codes for troubleshooting. My device has a light that flashes and and chart for reference. Think of it like a diagnostic system in ICU ventilators:

Everything is getting computerized these days.

My control unit produced a sequence of 7 flashes, which indicates that I have a faulty flammable vapor sensor (FVS).

The FVS is a relatively newer’ish invention that consists of a silicone type sensor that detects flammable vapors outside of the hot water tank. If you have a gas leak, you certainly don’t want to have an open flame feeding off that fuel. The downside of the sensor is that it can be trigger by other fumes in the vicinity such as paint fumes.

Check to make sure that you don’t have a gas leak.

The most critical reason why your gas control valve triggers an FVS error is that it might actually be doing its job. Do you have a gas leak somewhere? Make sure that you don’t smell fumes from natural gas, garage off gasses, or even open paint cans in the vicinity. Vent the area where your water heater is located. Only when you are certain that there is no dangerous situation should you proceed to make changes.

Reset the FVS.

Let’s say that there was a temporary trigger to the sensor. Maybe there was a spider that built a nest right on your water heater. Perhaps your dog had a loose bowel movement. Whatever. You can reset your control panel. Every device is going to be different. The user’s manual should have a section on resetting the device. Or try Google. That’s what I did.

I have a Honeywell type control panel. There is one on-off switch, plus a dial to control the water temperature. To reset my controls, I did the following:

  1. Flip the switch to ‘off’.
  2. Unplug the unit.
  3. Turn the temperature dial to ‘low’.
  4. Plug in the unit.
  5. Flip the switch to ‘on’.
  6. Modulate the temperature dial from ‘low’ to ‘very hot’ about 3-5 cycles.

At some point, you will hear a spark. The pilot light will subsequently light, and you will likely hear a whoosh where the flame ignites underneath the water heater. If your hot water heater stays on, then you’re home free.

You might have a bad vapor sensor.

Unfortunately after I performed a reset on the control unit, my water heater shut off after five minutes. My FVS is situation on the edge of the water heater in a plastic cover.

The sensor looks like a power socket plug.

25VS. The little guy that stands between hot and cold showers.

When the sensor detects a sensitive fume its resistance increases and closes the circuit. On average the working range of these resistors is somewhere between 9-45 kilo-ohms. I was able to test the resistance of my FVS using a multimeter, and mine was somewhere around 196,000 kilo-ohms! (196 mega-ohms). Clearly the FVS had simply gone bad.

Mega amounts of resistance indicates a bad vapor sensor.

One hack to get your hot water heater going in a pinch (DON’T DO THIS) is to install a resistor in the circuit. If you have access to a Radio Shack or electronics store, you can pick up a 15k-ohm resistor. Tie it into your hot water heater, and you will have bypassed the safety mechanism of your hot water heater.

Replace the vapor sensor.

If you have a bad sensor, the fix is easy—get a replacement and install it. Many of the big box chains like Lowe’s and Home Depot will unlikely carry these parts, but a specialized plumbing company might.

You can also find replacement parts on eBay or Amazon. I have a Whirlpool water heater, which is actually made by American Water Heater Company, whose parent company is A.O. Smith.  This is important because many of the replacement parts are interchangeable. Through some detective work, I found out that my flammable vapor sensor was also manufactured by Rheem. The part online was $25 with free shipping.

How much did I save?

Plumbing is a specialized profession (like gastroenterology). It may not be the most challenging line of work, but it can be dirty.  The local plumbing chain charges $150 per visit ($300 on weekends), $150/hr for labor, plus parts. This probably would have been about a $450 job. Plus the agony of calling the plumbing and potentially taking a day (or half day) of work off.

Not a bad trade-off, especially in post-tax dollars.

Priceless.

How much home maintenance do you deal with?

Do you want to get the latest Smart Money MD posts in you inbox?
Get the FREE Smart Money MD Financial Cheatsheet for signing up!
Tags:
  • This takes me back to my days when I installed these along with air conditioners with my grandfather. It’s nice to see another physician tackling some DIY projects.

    • Smart Money MD

      It’s all about our hourly rate and difficulty. I used to service my own AC unit (on 2nd story roof) until one of my patient’s husband ended up falling off and killing himself. For a couple hundred bucks , it’s not necessarily worth risking my neck fixing something. Even though I think that sometimes I do a more thorough job.