Water Heater Woes

Tevo · October 15, 2011, 05:18:50 PM

So on my 62 4106 the previous owner mounted the water heater in the bay hanging from the top of the bay and flush with the bay door. Meaning with the bay door closed, it was flush right up against the bay door, and had no vent. He used it recreationally, so he just opened the bay door whenever he was using hot water.

Being a fulltimer, that obviously doesn't work for me. So today I cut a hole through the bay door and put a floor register cover vent over the hole to finish it. Doing this, though, left about a 2 inch gap between the heater exhaust and the beginning of the backside of the register. Worried I might have exhaust venting throughout that gap into the bay, I took some sheet metal and fabricated an extension for the vent so that it tucks right into the register when the door is closed.

In theory, this works great. Problem is, (and there's always a problem, isn't there) the pressure relief valve is dripping now. It doesn't drip when I run the heater with the bay door open, but does it when the door is closed.

My only guess is that the exhaust is getting restricted making that extra 3 inch run or so to the exterior, and causing pressure to build up in the heater, which makes the relief valve leak. Does this make sense? Any other possibilities here? Any possible solutions to this?

I would just replace the relief valve, and I still may, but the fact that it doesn't leak with the door open makes me think it's something to do with exhaust restriction. Thoughts?

Lin · October 15, 2011, 05:59:03 PM

Is anything touching the relief valve when you close the door? Are you sure that there is not a minute leak or condensate that is evaporating when the door is open but not when the door is closed?

redbus · October 15, 2011, 06:06:28 PM

Do you have a fresh air intake for combustion?

bobofthenorth · October 15, 2011, 06:07:42 PM

I can't think of any logical connection between a water heater exhaust and the pressure relief valve.

Tevo · October 15, 2011, 06:09:07 PM

Quote from: Lin on October 15, 2011, 05:59:03 PM
Is anything touching the relief valve when you close the door? Are you sure that there is not a minute leak or condensate that is evaporating when the door is open but not when the door is closed?

The relief valve is back an inch or so so pretty sure it's not touching anything. I've been sitting and watching it go with the bay open and haven't seen a single drop come out. When closed it's dripping pretty good, though, so I think the flow would be evident even with some evaporation.

Tevo · October 15, 2011, 06:10:27 PM

Quote from: redbus on October 15, 2011, 06:06:28 PM
Do you have a fresh air intake for combustion?

No, it's just mounted like a standard RV water heater with the one vent for the exhaust. It is in the open bay so I would think it's getting plenty of air.

Tevo · October 15, 2011, 06:11:34 PM

Quote from: bobofthenorth on October 15, 2011, 06:07:42 PM
I can't think of any logical connection between a water heater exhaust and the pressure relief valve.

Hmm, well there goes that theory. Really odd that it's only doing it with the bay door closed though. If that's not it I have no clue what it could be.

bobofthenorth · October 15, 2011, 06:30:07 PM

Could the exhaust be blowing directly onto the relief valve? That might warm the valve enough to cause it to open.

Tevo · October 15, 2011, 06:51:09 PM

Quote from: bobofthenorth on October 15, 2011, 06:30:07 PM
Could the exhaust be blowing directly onto the relief valve? That might warm the valve enough to cause it to open.

It's routed so it is blowing into the register, but that's a good point. Maybe there's just enough restriction there which is causing the whole area to get hot, causing it to open?

bobofthenorth · October 15, 2011, 07:18:50 PM

The valve is temperature & pressure activated so if it is getting hot that could cause it to open. It may also be opening prematurely so a replacement might solve the leak. If you've got some kind of remote thermometer you could set it up in the bay strapped to the valve to see what is actually happening when the door is closed.

Seayfam · October 15, 2011, 10:01:07 PM

First off, is this a RV style hot water heater? Second, does it still have the hinged door on the water heater? If the answer is yes to both, then your question is yes on the restriction. The way the RV style hot water heater works is; the nozzle and igniter light the flame at the lower portion of the water heater, the exhaust runs through the hot water heater heating the water and then out the upper portion of the unit venting through the grill on the door. If you have a extension mounted on the bay door to the water heater, you are creating enough restriction to let the exhaust heat the water that much more. If the hinged door is still mounted on the hotwater heater, I would remove it and build a air tight seal to go around the whole square portion of unit that would seal against the bay door and then install a larger grill in the bay door. You don't want to take any chances with carbon monoxide! (It will work up through the bay and into the cabin)

Tevo · October 16, 2011, 07:07:09 AM

Quote from: Seayfam on October 15, 2011, 10:01:07 PM
First off, is this a RV style hot water heater? Second, does it still have the hinged door on the water heater? If the answer is yes to both, then your question is yes on the restriction. The way the RV style hot water heater works is; the nozzle and igniter light the flame at the lower portion of the water heater, the exhaust runs through the hot water heater heating the water and then out the upper portion of the unit venting through the grill on the door. If you have a extension mounted on the bay door to the water heater, you are creating enough restriction to let the exhaust heat the water that much more. If the hinged door is still mounted on the hotwater heater, I would remove it and build a air tight seal to go around the whole square portion of unit that would seal against the bay door and then install a larger grill in the bay door. You don't want to take any chances with carbon monoxide! (It will work up through the bay and into the cabin)

Yes, it's an RV water heater, but I took the front door off to mount the extension. The way I have it is I used folded thin gauge sheet metal to build an extension that is attached to the existing sheet metal exhaust port. It's three sided, just like the existing port, and is just long enough so it tucks into the back of the register (which is why I had to take the door off. I don't believe CO is a problem...being paranoid I stuck a CO/LP detector in the bay about 8 inches away to see if I was getting any leakage and am showing no increase in PPM. And I seem to be getting a fairly good flow out the register vent. I suspect bobofthenorth's heat idea might be right though, and am going to pop a remote oven thermometer by the valve today to see. If it is, it's likely still a restriction issue, but heat moreso than anything. That may call for a bigger vent like you suggested either way though. Before cutting a bigger hole, though, I'll probably just replace the valve just in case. Always hoping for the easy fix.