Water heater pilot light won't stay lit in my attic

Question

So I've heard most of the answers in other similar threads around here but this one was new to me.

I recently bought an older house and it has a natural gas water heater in the attic. Nothing terribly unusual about it. It's been running relatively well until recently, when the pilot light started to go out on a semi-frequent basis. I have a home warranty we got when we purchased the house, so I paid the money for a service call and the guy who came out told my wife that there was nothing wrong with the tank, that the attic was getting too hot and it was making the tank shut the pilot light off.

We had a large tree removed from one end of the house. That end also has a non-functional fan (we think they only had powered fans to exhaust hot air) so it's possible the attic is getting hotter than it did before. The bank (who rehabbed it after a repo) added two wind turbines to the main part to exhaust air. This plumber said they didn't move enough. He suggested putting a box fan near the tank to help keep it cooler.

This doesn't make any sense to me, and it sounded like he was trying to get the warranty company out of a repair. Has anyone heard of such a thing?

Answer 1

Your plumber may be right, and from my experience, it is uncommon that he'd know that (unless, like you said, he was trying to get the home warranty company out of a bill and happened to stumble on the cause).

When your attic gets hot, and there is bad or no circulation, according to Charles' law, the pressure in your attic increases. If it gets hot enough, it can increase high enough that it can suffocate the pilot flame. So if you have no circulation in a hot attic, you can definitely snuff out the pilot flame. Replacing the water heater may not fix the problem. But probably neither would circulating the high pressure air in place with a box fan.

Check your venting situation, especially the passive elements. For example, if you have soffits, make sure they have not become clogged with blown insulation. I would take a blower of some sort (a shopvac that can be reversed for example) and blow them from the outside. Also, look from inside the attic and check what the situation is. If you've had recently blown insulation, it could definitely have caused a problem.

So my suggestion - clean your soffits and evaluate your passive ventilation. Resist the impulse to add active ventilation unless you know what you are doing (they can cause issues). If you can't figure out the problem, it may need the experience of an experienced roofing contractor who understands how to calculate your roofing needs and install additional ventilation. It could be that your two turbines are sufficient, but you are not getting enough air in through soffits and other inlets, for them to pull out. You can google for various formulas to consider how many feet of soffits or ridge vents/passive ventilation you need. If you have no soffits and only a non-functional active fan to push air in, that's probably your problem. I'd add soffits.

By the way, it is possible that as your water heater has aged, it is more sensitive to the increased pressure. This I don't know, I am just theorizing, and someone with practical experience should chime in. Replacing parts or replacing the heater may help or fix the problem, if you are just on the edge of the issue. If you've already fixed the issue, it would be interesting to learn what solution you finally arrived to.

Edit: Finally found a reference to back up my answer! It's a Rheem/Ruud technical service bulletin, in case the link dies, but I don't see a bulletin number on it.

Attic Ventilation and Pilot Outage in Gas Water Heaters

Answer 2

Charles Law? No way an attic is pressure tight such that it would be higher than pressure in gas line. Thermocouples can’t sense pressure anyway. They are to send a signal to shut off the gas if they get too cool, not too hot.

I’ve heard poor circulation could mean all the oxygen is used up, but the heater is vented like a fireplace.

I suspect that the thermocouple works off temperature differential and if air is too hot is senses low differential and sends signal to close valve.

Answer 3

There's two common causes that I know of for a pilot light to go out, and this isn't unique to water heaters. It can be blown out by moving air, or be extinguished by a safety device detecting a depletion of oxygen.

Given the situation it is likely the pilot is just getting blown out by air moving through the attic. The old tree may have blocked the wind from blowing across the attic with sufficient force to blow out the pilot, with it gone there's more wind. Also possible is that the changes to the attic ventilation caused changes to how the air moved, such that if the wind blows just right and/or the attic gets hot enough then there's enough movement of air to blow out the pilot light. If the pilot light is getting blown out then a fan could only make it worse.

It is possible, though perhaps unlikely, that the water heater is running out of oxygen and the ODS in the water heater cuts the fuel supply. I don't know when ODS became a feature on water heaters but it is possible a 20+ year old water heater has one.

The acronym ODS is a bit of a misnomer in most cases as this stands for "oxygen depletion sensor". In newer gas fueled appliances the pilot light system is structured such that if there's not enough oxygen the flame will "bend" such that it no longer heats the thermocouple that holds the fuel valve open. Without a sufficient flame the thermocouple cools, the fuel is cut, and the pilot goes out. There's no ODS to replace if this is the case, the pilot light or something related to it might need replacing or there just needs to be more oxygen.

If the attic is hot enough then it could thin out the air enough to trigger the ODS which then extinguishes the pilot. The heat won't thin out the air enough that people can't breathe but it could be enough that the fuel for the appliance isn't burning completely and this creates a fire hazard. A fan is not likely to help in this case because the fan would just move the hot oxygen depleted air around the attic. The entire attic would need to be cooler not just the water heater, and blowing the same hot air around isn't cooling anything.

Those are my theories anyway based on experiences with pilot lights going out. Blocking any wind from getting to the pilot should be simple enough. If there's an actual separate device in the water heater called an oxygen depletion sensor then that could be checked or replaced to rule that out. If it is just plain too hot in the attic then a fan blowing on the water heater sounds like a rather ineffective means to resolve the issue, and if by chance it does cool the water heater then it could also blow out the pilot.