Rinnai R53 - Intermittent Flame Failure

mrgem

Our 10-yr-old Rinnai R53 (LP) started getting occassional Error Code 12s recently after 10 years of excellent performance.

Since I was overdue for a checkup on all my domestic plumbing, I contacted a local plumbing/Heating guy and asked him to come out and do a service on both the boiler and our R53 tankless water heater. When he arrived, I told him that the unit had been loosing flame every time you'd try to fill the bath after 5-10 minutes. Other hot water appliances (kitchen sink, bathroom sinks, etc.) worked fine. Only the bathtub was affected. I'm sure it flows a lot more than the other appliances and this is why it fails.

The plumber inspected all the Rinnai's electrical connections, cleaned the flame rod and burner and told me to clean the heat exchanger -- by flushing it with vinegar for an hour and cleaning the filter. I did so and am still seeing the same symptoms and the same error code. Should I replace the flame rod? Isn't there some flow sensor that might cause this?

The house is a weekend cabin and only sees 10-12 24-hour visits a year -- so the unit gets very little use. I should think that it is extremely "low mileage" for its age, so I am surprised to see it having problems.

I'd hate to have to replace it if I don't have to.

I should also note that the house is in a very rural area, and there are no Rinnai Factory Qualified plumbers within 75 miles -- so it is tough (and expensive) to get someone out there.

Thanks for your input.

rick in Alaska

Does it vent out the side wall or through the roof? I have been having similar issues with ones that are vented through the roof getting water vapor back down into the burner area because of the pipe not being insulated through the attic area and causing condensation in the air intake pipe. Owner is trying to get to attic space to make sure pipe is insulated.
Also, I wonder if you might have a regulator problem where the pressure starts changing after it runs for a while? You would need to do a pressure test with it running to check this.
Rick

Jack

Drop the inducer motor and inspect/clean it. Careful in replacement that you get the tongue in the back before lifting the motor to attach the two screws. While the motor is out get a light and see if the diffuser plate under the burner is clear. I have trouble getting my fat head in there, so you may need an inspection mirror. Rick's suggestion on the gas pressure check at high flows is correct. You need a manometer to do this test. Lift the vent off the top and look down at the burner tray. If there is a lot of debris or precipitant (from moisture that has come down onto the burner, again to Rick's point) the burner tray must be removed and the individual burners cleaned. The R53 has 16 identical burners in its rack. IF there is precip. on the burners it happens right where the flame rod and sparker are. With the burner tray out there are four screws that hold the burners in the rack (two in the back, two on the sides). Remove them and carefully remove the strap. take the 3 burners in the left side of the tray and move them to the flame rod/sparker area. Swap the position of the burners. Reassemble and try it out. DO NOT attempt any of this without proper gaskets in hand for the reassembly.

mrgem

rick in Alaska said:

Does it vent out the side wall or through the roof? I have been having similar issues with ones that are vented through the roof getting water vapor back down into the burner area because of the pipe not being insulated through the attic area and causing condensation in the air intake pipe. Owner is trying to get to attic space to make sure pipe is insulated.
Also, I wonder if you might have a regulator problem where the pressure starts changing after it runs for a while? You would need to do a pressure test with it running to check this.
Rick

Rick -- Thanks. I'd also read about restrictions on the vent causing flameouts.

However,the unit vents through a side wall -- and started gettting the error codes in early August -- weeks before the temperature got cold enough to see ice forming.

mrgem

Jack said:

Drop the inducer motor and inspect/clean it. Careful in replacement that you get the tongue in the back before lifting the motor to attach the two screws. While the motor is out get a light and see if the diffuser plate under the burner is clear. I have trouble getting my fat head in there, so you may need an inspection mirror. Rick's suggestion on the gas pressure check at high flows is correct. You need a manometer to do this test. Lift the vent off the top and look down at the burner tray. If there is a lot of debris or precipitant (from moisture that has come down onto the burner, again to Rick's point) the burner tray must be removed and the individual burners cleaned. The R53 has 16 identical burners in its rack. IF there is precip. on the burners it happens right where the flame rod and sparker are. With the burner tray out there are four screws that hold the burners in the rack (two in the back, two on the sides). Remove them and carefully remove the strap. take the 3 burners in the left side of the tray and move them to the flame rod/sparker area. Swap the position of the burners. Reassemble and try it out. DO NOT attempt any of this without proper gaskets in hand for the reassembly.

Thanks. I will check the inducer motor and burner -- but will likely have to bring a pro out to do it -- as I am just knowledgable enough to get myself in trouble.

Just had my plumber/heating guy out there to replace a boiler at the same property ($5300!!) and he commented that while he was not Rinnai-factory certified -- he'd had plenty of experience with them and would be happy to work on it (if I paid him for 4-hours of travel time). The local guys in that area want $50 more an hour than he does -- so even with travel time -- I'm probably better off bringing him in.

I will print off your comments and share with him. Looks like time to suck it up and get a pro involved.

Thanks again for your input.

Jack

I was on the phone today with Rinnai tech service on another matter and asked about your situation. His suggestion was to see if there is any fluid in the clear tubing at the bottom of the gas valve. If there is the valve is shot. As well, given the long period of good operation, perhaps the vent condensing onto the burners has built up to this situation.

rick in Alaska

I had one that had the clear tube with water in it and had to change out the assembly. This one was because of water that had got into the top and "flooded" the top of the burner assembly and let water get in to the tube. I am thinking the tube needs to have a T with a drip leg on the bottom to keep the valve from getting damaged. Watta ya say Jack!
Rick

Jack

There is a nipple that projects into the bottom of the burner chamber. The tubing connects to the bottom of it. It takes quite a lot of water to be able to get up to the top of that connection. Your suggestion makes sense to me, but the real problem is prevention of the water being there in the first place. Over the years water in that tube meant a new gas valve.

mrgem

Great information, gents.

I'm going up there this coming week. I'll let you know what I find.

Thanks again for all your help!

mrgem

Well, spent a couple of hours playing with it this weekend and while I did learn some interesting things about the way it operates, I still don't have a definitive reason the flame is going out.

There is no water in the tube running to the bottom of the gas valve. The vent, which runs slightly uphill after a 90 on the top of the unit has a proper drain just after the 90, so that looks good.

One thing I did notice is that with the cover off and looking straight into the combustion chamber through the window, watching the burner light and heat water, something may be amiss. The unit has 16 burner "rows" that run from front to back as you look through the glass. The two or 3 rows directly in front of the sight glass have gaps in the flame pattern. All the burner rows to the left and right seem to have a solid row of blue flames their entire length. The couple of rows directly in front of the glass have "gaps" in the flames in several places. So, I am thinking this may be indicative of a dirty or damaged burner.

Someone suggested I have the propane company come out and check the gas pressure going into the house- just to make sure that meets the appliance requirements. I guess having the burners cleaned and the gas pressure checked is next.

Thanks again for all your advice. Stay tuned...

Jack

Seems to indicate condensation is getting onto those burners in front of the flame rod/sparker. Any flame instability there will drop the unit out. Exactly how is the vent oriented? Vertical how high? Horizontal how far? Does the Horiz grade to the outside? Is the vent condensate trapped/drained? It sounds to me that over time a small amount of condensate or rain water has gotten onto the burners and boiled off and has built up to the current situation.

mrgem

Jack said:

Seems to indicate condensation is getting onto those burners in front of the flame rod/sparker. Any flame instability there will drop the unit out. Exactly how is the vent oriented? Vertical how high? Horizontal how far? Does the Horiz grade to the outside? Is the vent condensate trapped/drained? It sounds to me that over time a small amount of condensate or rain water has gotten onto the burners and boiled off and has built up to the current situation.

Thanks. I had the gas company come out and test the pressure -- per my plumber's instructions. The pressure was a little low -- but raising it has made no difference.

I've spent some more time studying the sequence of events and watching the burners through the little window. As someone here noted, there are 16 burners rows each with 15-20 tiny orifices -- each with its own flame.

When the unit first fires up, all the burners and all the orifices are burning just as you'd expect. After 7 minutes of running the bathwater (it is consistent in that time period), the 2 or 3 burners directly in front of the window start to go out. They sputter a few times (all the other rows are burning perfectly) and then the unit shuts down and gets the error code 12.
I spoke to Rinnai and they suggested I swap out the flame rod and the flow sensor.
I'm willing to try just about anything at this point, but am beginning to think I should consider replacement of the whole heater.
Thanks for everyone's suggestions.

Jamie Hall

I'll go with @Jack 's comment: water -- condensate most likely, but it could also be a leak which opens up when the unit gets hot -- is landing on that group of flame orifices.

Jack

Jamie likely has it here. If there is condensation coming back from the vent...somehow, and it has happened over time, it is likely that the fins on the HX, through which the moisture must pass before getting to the burners are, crapped up ( "Crapped up" was actually a term we used to use on nuclear power plant shut downs when someone would exit the containment area and carry some radiation out with them. Verboten in the extreme) That was just an aside, but an aside from one who has a half life of his own. If you lift the vent pipe off the unit, you can look down onto the top of the he and see if this has happened. If it has you are creating hot spots which will lead to a leak. If the fins are clear, move the burners. It is not that hard to do, but do get the gasket kit prior to going forward. So, lift the vent and report back.

sacryheating

I would suggest pulling out the burners and blowing them out with 100psi compressed air and also you may need to run a torch over the burners also look in the burner holes where the orfices go in and make sure there is not a spider web in there