Water heater problem/question.

I have a water heater that is giving me Fits.

It’s electronic ignition, power vented propane gas.

It had been working fine for about 5 years.

The symptoms (water is currently cold) - It will electrically ignite the pilot and burner and run for about 3 minutes. The burner will then turn off for about 30 seconds and the electric ignition will re-light it again. Now it will stay lit for about 30 seconds and turn off. It will not re-light. The igniter will not turn on (glow red).

The only way it will re-light is to unplug the 110v and let everything reset. It will then repeat the 3 minutes on, 30 seconds off, 30 seconds on and then dead.
The power vent/exhaust stays on during the entire process. Never shutting off.

I have replaced the thermocouple and igniter.

The thermostat is set to medium and the circuit is closed.

I think it’s time for a plumber.

I think it’s time for a professional too. It may be a safety feature triggering shut down.

Yeah. I just get frustrated when I can’t figure something out as simple as a water heater. Though I have never had an electronic ignition/power vent before.

It has a pressure switch to shut it down in case too much builds up. That circuit is closed. ie, power is flowing through it. It also has a switch to detect too much moisture in the exhaust gas. That circuit is closed, power is flowing through. Another switch for temp in the blower. Closed.

I’m running out of stuff to test. I guess it may be the gas pressure regulator or the gas valve itself. I don’t really have a way to test any of that.

It’s interesting that it is so consistent. That in itself should be a dead giveaway. I’ll call a plumber.

I’m still interested in any ones theories though.

Thanks

You will have to find a plumber that wears suspenders, as the common ordinary plumber will not know much about electronics.
Maybe a HVAC professional?

I had a similar problem with my furnace. It turned out that there is a sensor that makes sure of proper ignition. It got too much carbon build up on it. It’s just a little wire that sticks into the flame. A scrub with steel wool did the trick.

Does the heater have anything that gives fault codes? My furnace has an LED that blinks a certain number for each different problem.

I’m guessing that you are talking about the thermocouple. That’s the first thing I checked (just replaced it actually)

No LED’s on my water heater. Got a wiring diagram on it that has helped… Well at least I know what I testing.

I have an old friend that works for a plumbing and heating company. I haven’t talked to him in a while, but I’m going to give him a call. (Just remembered him actually).

Thanks

If you can identify all of the safeties on the heater, you could take them out of the safety circuit one by one until you find the one that is causing the problem.

One clue is that it has one auto reset and then goes into manual reset mode. I’d guess flame sensor also - once it gets up to operating temperature it fails; the second burn time is shorter becasue the safety is already warm.

I’d also check the flue vent to make sure that it is actually clear. The exhuast may not be going up the vent.

I’ve been testing the safeties to see if they break the circuit after the failure. Though I suppose they may instead close a circuit to shut the thing down. Or reset so fast I miss it.

Flue is fine. One thing is odd though. The blower, or power vent, runs constantly. It used to only run when the burner is on. I need to look closer at that. Symptom? Cause? Who knows.

I may pull the thermocouple, put a torch to it and see if I can get a voltage reading. And see if it fails after a bit. Since I did just replace it, I doubt that’s the problem.

Ooooh. First I’ll check the old one.

One thing for sure. I don’t trust it. Gas is off when I’m not physically there to watch what it’s doing.

Are you sure there is actually a thermocouple?

The reason your draft inducing fan is running not stop is because the thermostat isn’t being satisfied. In other words, a “call” or “demand” from the thermostat is always present.

The obvious reason that’s the case is that some safety in the system is shutting down the burners prematurely; before the stat reaches setpoint. Normally your furnace “cycles” on your thermostat. Yours is cycling on a safety—the safety is interupting the call for heat.

My guess is that the flame sensor is blind. As Paintcharge pointed out, it’s likely the “flame sensing” is awry.

It could also be the pressure switch. It is designed not to sense not “too much” but to sense that there is pressure greater than baromtetric pressure—evidence that the draft fan is working.

If you’ve successfully and correctly determined that the safeties are closed (And the best way to do that is unplug them and “jump them out” one by one. (They can sometimes intermittently open and close and the best way to avoid that is to jump them.)

Based on what you’ve given us I’m guessing flame sensing too. Post the manufacturer and model number and we’ll tell you what else to look for.

I had a similar symptoms on my furnace a few years ago when my earthquake valve tripped. (I bumped it) and shut “off” which turned out to not be very off.
The furnace would try to come on but there was not enough gas to satisfy the flame sensor and it went back off. To my eye the flame did look a little small.
I figured all this out after replacing many parts and much banging of head.
BTW it can’t be the pressure or flow switch, as the gas valve will never open if there is insufficient air flow.

I didn’t get a chance to test anything last night. I’ve been dealing with snow.

First off, thanks for all the suggestions.

It’s some sort of flame/heat sensor that the pilot light heats up. The flame from the pilot light heats it up to the point that it glows red. I’ve always called this a thermocouple. I have replaced it. That’s the first thing I did. I guess it could be bad right out of the box.

I’m suspicious of the pressure switch as well. Especially since the vent fan runs continuously. It’s going to be hard to figure out how to jump it as there are 5 wires going to it. I’ll have to study the wiring diagram a bit closer. It’s very odd how it is installed in the water heater. It’s some sort of screw in, snap fit. I have yet to figure out how to remove it, but I can unplug it and get to the wires.

hmmm….

I’m at work at the moment, so I don’t have the model number. It’s a Bradford White 50 gallon. High altitude propane electric ignition with a power vent.

Ahh. I guess it’s not a thermocouple. The ignitor/flame sensor/pilot assembly looks very much like this. It may actually be this model. I’ll get the real deal model numbers when I get home later today and take a picture of it.

In the mean time. How would I test it? I suspect I’ll need a digital multimeter.

RE: pressure switch

I’ve seen people replace pressure switches when they were simply doing their job.

IOW, sometimes there is a restriction of some sort in the flue that the pressure switch is reacting to. A common way to troubleshoot that is to take the flue pipe loose at the appliance and see if the problem goes away. This will only be possible if the flue pipe is not glued to the fan housing, but rather with a set screw or rubber collar.

Read This: While testing this out for the 3 minutes or so it will take to determine in the flue has a restriction, flue gases (read: carbon monoxide) will be entering your home. That will be ok for the couple minutes to troubleshoot the flue, but you cannot leave the flue unconnected to the appliance.

One other thing…

Get the model number on the gas valve too. Honeywell makes a “Smart Valve” that is an electronic gas valve. I hate them. (and I’m a Honeywell fan)

Some of the Smart Valves had problems with the white plastic connector that snaps into the top of the Smart Valve. It would be loose and not make consistent connection to the electronics in the valve. Did I say I hate them?

The only solution I know for them is to replace the valve, unfortunately.

The flue is all of maybe 8’ long. It has one elbow in it and I haven’t glued anything together at this point. So checking it for obstructions is not tough.

Is there a way to test the flame sensor?

eta - I suppose if the pressure switch is malfunctioning ANY back pressure may make it fail? I guess I should try your method and completely disconnect it.

And I’ll check out that valve. Thanks

I think that the air intake (“combustion air”) comes from the perforated holes in the outer shell on the heater. (iirc…)

Is there any restriction to those holes? Because some pressure switches read what’s called “differential pressure”; meaning not just the exhaust but the intake can’t be obstructed.

Sounds like faulty flame-sensing.

The sequence of operation should go something like this:

  1. A call for heat. (thermostat indicates water temp is below setpoint and closes contacts)

  2. Power draft starts.

  3. Pressure switch proves power draft started, possibly followed by a short purge period.

  4. Gas is allowed to the pilot light and spark ignition is initiated.

a. If pilot lights and is proved by flame sensor than main burner ignition will allowed.

b. If pilot doesn’t light or flame sensing fails then flame safety will lock out immediately or after a predertimed number of retries. Lockout will likely require power reset.

  1. Main burner ignition is allowed but flame sensing continues. If flame sensing is lost during burner run then lockout will occur, requiring power reset.

  2. Call for heat is satisfied. Burner turns off. Powered draft may run for a post-purge period then shut off.

It sounds like to me you’re at Step 5 and losing flame sensing. Paintcharge has a good suggestion. Also that pilot assembly must be properly grounded for the flame rectification circuit to complete, look for rusty connections. Beyond that you probably need a professional.

There might be a clue in the fact that the burner runs for a few minutes THEN loses flame sensing. Thermal expansion might me causing the pilot assy to lose a firm ground?

I’ve read your OP again with a little more care…

Amend Step 5 to include retries… then lockout.

Amend spark ignition to hot-surface ignitor(glowcoil).

If you’ve already replaced the WHOLE pilot assy make sure connections are tight, then call a professional.

Yep, replaced the whole assembly.

I understand now that a failure or two locks down the whole system. Makes sense really.

I hope to be able to get ahold of an old friend that works for a HVAC company. It just sucks trying to get service people out to my house.

It is possible, but less common, to lose flame sensing 3 minutes into a cycle.

Most often when flame sensing is lost it happens at ignition—typically at around 2-5 seconds.

You sound pretty sharp on these type things, and if you have a volt meter we can give you more direction if you have the manufacturer and model number (including the gas valve), although an experienced tech would serve you better.