I Think I Need a New Gas Valve

We have a cabin with an older Williams gravity floor furnace. We bought the cabin this year. The furnace hasn't been used in 20 years, maybe more. The specs are:

Model number: 45FF-H
Serial number: 2541
Equipped for: LP gas
Input: 45,000 BTU HR
Manifold pressure: 10 0 IWC
Min. Gas Supply pressure: 11 IWC
Design complies with ANS1Z21.48 floor furnace: B1988
Date code: 37.90

I can get the pilot to light, and stay lit. It's a millivolt system, so the thermopile is generating enough current to keep the pilot valve open, at least. However, the main gas valve will not turn on. I've tested continuity in the thermostat circuit, and it's good. The thermostat is a 750mv type.

The gas valve, which I photographed in the crawlspace, has a model number VS821A1277. It came up as a Honeywell model when I googled it. Some of the electrical connections look pretty corroded, but there is continuity between them.

I'm not sure if the thermopile is generating enough current to open the gas valve, or if the gas valve even works anymore.

I called Williams to get info about replacing the valve, and a man there said it could be an older "IT" valve, which can't be replaced because the connections are different. I'm not sure what an IT valve is. I also called Robertshaw, and a man there looked up and found the Honeywell model, and said a 710-502 valve with a L.P. conversion would work. I haven't heard back from Honeywell yet, so all I have is a bit of conflicting information between the two people I spoke with.

Here are some photos:







Any suggestions on how I can proceed? Everything I've learned about floor furnaces has been in the last 2 weeks.

EDIT: I do have a great friend there who has experience doing this kind of work, and he'll help out. So I'm not alone in this, but it's up to me to research the answers and get the supplies.

Hi,We have a cabin with an older Williams gravity floor furnace. We bought the cabin this year. The furnace hasn't been used in 20 years, maybe more. The specs are:Model number: 45FF-HSerial number: 2541Equipped for: LP gasInput: 45,000 BTU HRManifold pressure: 10 0 IWCMin. Gas Supply pressure: 11 IWCDesign complies with ANS1Z21.48 floor furnace: B1988Date code: 37.90I can get the pilot to light, and stay lit. It's a millivolt system, so the thermopile is generating enough current to keep the pilot valve open, at least. However, the main gas valve will not turn on. I've tested continuity in the thermostat circuit, and it's good. The thermostat is a 750mv type.The gas valve, which I photographed in the crawlspace, has a model number VS821A1277. It came up as a Honeywell model when I googled it. Some of the electrical connections look pretty corroded, but there is continuity between them.I'm not sure if the thermopile is generating enough current to open the gas valve, or if the gas valve even works anymore.I called Williams to get info about replacing the valve, and a man there said it could be an older "IT" valve, which can't be replaced because the connections are different. I'm not sure what an IT valve is. I also called Robertshaw, and a man there looked up and found the Honeywell model, and said a 710-502 valve with a L.P. conversion would work. I haven't heard back from Honeywell yet, so all I have is a bit of conflicting information between the two people I spoke with.Here are some photos:Any suggestions on how I can proceed? Everything I've learned about floor furnaces has been in the last 2 weeks.EDIT: I do have a great friend there who has experience doing this kind of work, and he'll help out. So I'm not alone in this, but it's up to me to research the answers and get the supplies.

How does a gas valve work?

In a nut shell: The gas valve’s thermal well senses the temperature of the water inside the water heater. If the temperature of the water is below the desired temperature setting indicated by the dial on the gas control valve, the gas valve will open the gas supply line, feeding gas into the burner chamber via the burner tube (aka burner manifold tube) so that the burner will be lit/remain lit by the pilot assembly’s ignitor. During this process, the pilot assembly and thermal well send electric signals to the gas valve to ensure that the unit is operating safely, and to tell the gas valve when to stop allowing gas into the burner assembly.

What should the light on a gas valve do?

If your gas valve has a status light, the light should normally be green or blue. Also, it should flash, typically once every four seconds, indicating that the water heater is idle; alternatively, the light may also alternate from bright to dim, indicating that the unit is heating water. If the light is off, there is no electrical power to the unit; if there is any other flash sequence or the light is red, there is likely an issue with your unit. For details regarding your specific unit, please refer to your installation manual, where you can typically find a diagnostic and troubleshooting chart; some gas valve models may also have a label with flash codes and explanations directly on their face plate.  

How do I know if my water heater’s gas valve needs to be replaced?

The most common indications that your gas valve needs to be replaced include:

-      Gas valve related flash code (see Flash Code Section below)

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-      No hot water or inconsistent hot water (although this could be caused by many other issues)

-      If you have changed the pilot assembly and still do not have a consistent flame, it is probably the gas valve 

How much do replacement gas valves cost?/Are replacement gas valves expensive?

This depends on three major factors: the age of the unit, the size of the unit, and the availability of the gas valve.

The cost of a residential gas valve is typically anywhere from $110.00 to $250.00 (or more) each. Prior to contacting a service provider, be sure to check and see if your water heater is still covered under warranty; during your phone call to the manufacturer, they may be able to confirm the diagnosis of a faulty gas valve and send you a replacement part. If your unit is still under warranty, they typically send the part for free, with the option to add expedited delivery for a fee.

The average gas valve replacement requires a technician to be on site for 45 to 60 minutes. In the event that you are responsible for the labor costs, a simple way to save some money of your service call will be to drain your water heater prior to the technician’s arrival; this way, they will be able to verify the faulty gas valve diagnosis, remove the old gas valve, install the new gas valve, re-fill your unit, check for gas leaks, and ensure that your unit is functioning properly without having to wait for the water to drain.