On demand water heater during cold weather

katsandogz

Hi,

I've owned a Rinnai RV53, propane on-demand water heater since 2012 and generally I am very happy with it. I live in VT and when temps get into the single digits and below, I get a code 12, flame failure. My heating and cooking are also on propane, all working properly. I've done some research and the only thing that seems to make sense in my situation is the venting. The unit is wall mounted in a well insulated crawl space basement in which the temperature does not go below 40 deg. I run an electric heater next to it when it is as cold as it is now, -20 last night. It is vented through the 6x6" rim joist and the 90 bend comes right off the top of the unit. I am thinking the problem is related to condensation and, if that were true, what would be my options? Any other ideas? Thank you.

aircooled81

I looked at a propane vapor chart, on engineer tool box website. It looked like at 50*f to 0*f, there was a 60psia drop.?
Not certain here, but is it possible cold propane storage can drop the pressure low enough to prevent proper ignition.
Where i live, it doesnt get that cold so this theroy doesnt need to be implicated.
? Just an idea as to why the unit doesn't fire on cold days?

aircooled81

Btw, i like the condensation idea... But the prepurge of the unit might be enough to dry it out before it Attempts combustion. When you look into the sightglass before firing on those cold days, are there beads of water forming on its surface inside?

katsandogz

Thank you for that input. Shortly after I posted, at -2 deg, the hot water came back. I attribute that to the sun which has been hitting that vent outside for a few hours now. That has happened before. When the sun goes away I will lose it again. Tonight. I have never seen beads of water on the sight glass, nor have I seen water anywhere inside when I remove the cover. I think I have noticed, in the past, moisture on top of the unit. Someone wrote about drilling holes. I doubt I have the clearance to get a drill in there and I don't know what I'm doing anyway.

hot_rod

What size tank and how much LP is in it? In extreme cold the LP may not be vaporizing under full boiler fire. The sun on the tank may be warming it enough during the day.

hot_rod

http://www.documentation.emersonprocess.com/groups/public/documents/bulletins/d4500147t012.pdf

katsandogz

It's a 100 gal tank which has never been a problem no matter how cold--1" black iron piping running through the basement. I have a direct vent propane heater and cook stove that runs off it as well. It was recently filled. It's on the north side of the house so doesn't really react to sun. It's a balmy 6 deg right now and the Rinnai is working fine. Tonight will be another story--going down to -10. Thanks for your input!

aircooled81

Direct fire, high btu, on demand water heaters, they require a lot of btu's. The stove and other appliances dont fire at the same rate as these do.
May i reccomend a heating contractor (our yourself should you feel capable) test the inlet gas pressure and firing pressure when the outdoor temp is soo low. If the gas pressure falls well below the requirement for this appliance, well then no flame.
The lack of moisture in the burner section leads me to beleive condensate is not wetting down the ignitor. Typically inside these models, condensate runs around in there all the time and is directed to a drain.

katsandogz

Thank you aircooled. That is sound advice and I intend to follow through. I have had a call in but getting a plumbing/heating person in VT when it's this cold is like trying to get one during hunting season so I was hoping to pick some brains. The rinnai is first in line on the gas pipe so wouldn't a lack of pressure affect the other two appliances as well? My direct vent furnace is last in line and puts out 30,000 btus. Anyway, I'll get someone up here eventually and if there is an answer to the problem, I'll post it back here. There is not enough info on this topic on the Web right now.

aircooled81

I sincerely hope this wh works for you through the cold evenings and mornings. I'll bet its tough right now to get a heating mechanic or plumber right now.
The only other idea i have is for you to contact the company that provides your propane, and posibly services it. Let them know you are not certain you are getting adequate pressure delivery through the cold evenings and see what they may have in mind to help.
Good luck,

katsandogz

Mystery solved. After checking my manual again and consulting my gas provider, what is needed is a condensate drain, a simple fix I can do myself. Sample photo. Temps are in the 20s now so hot water is running.