Rinnai R53i - Code 12

agt

Unit will provide hot water most of the time so long as we leave our single handle faucets at about 1/2 water flow. When I try to use full hot water flow, the fan comes on and I have a flame for about a second and then code 12 comes on a few seconds later. When I use a single handle faucet at about half available water flow the unit works most of the time but if I then increase to full flow the flame stops and I get code 12. There is the odd time that with a single handle faucet being used at half water flow it will show a good amount of flame for 10 seconds or so and then the flame drops down considerably and within 5 to 10 more seconds the flame goes out and we end up with a code 12 again. When using our only dual water faucet, I can turn the hot water tap to full and I get hot water on a consistent basis.

So far I have purged the unit with 4 gal of vinegar twice. I cleaned the inlet water filter. I have replaced the electrode, the flame rod , the gasket as well as the igniter. I have cleaned the heat exchanger. I am using a new combustion fan. I have checked the venting to make sure all connections are secure. I have checked the water flow turbine to make sure that it is turning freely and that there are no restrictions. I don't believe that there is any gas pressure problems involved with this situation and there is no water seen in the tube below the gas valve. Also checked the immersion sensor on the hot water exit tubing and it was clean.

At this point, I can only surmise that the problem could be related to a malfunctioning water flow servo-sensor.

The unit being 11 years old I am not sure if it would be wise to spend more money at this stage.

Hopefully someone can help me out with some suggestions as what the problem might be.

Jack

What was the condition of the HX just above the flame rod? How is the unit vented and have you inspected it for obstructions? Also, if you pull the burner tray you will notice there are 16 identical burners in the rack. On the 53 the 3 burners at the flame rod sparked fire every time. Those to the rat are the mid range and high fire is those on the left. Any time I have had issues with 12 on those units I will rotate those low fire burners to the left and put the left hand burners by the sparker/FR. there is a strap on the back of the burner tray with four screws that hold the rack together. Make sure you have new gaskets for the burner tray and FR/sparker. Check your electical connections. The water heaters rarely have a ground issue as they get a secondary ground through the water lines, but maybe there is a loose connection.

agt

The condition of the HX above the flame rod had a small amount of dried up residue from condensation. The venting is horizontal with one 90 degree plus about 14 feet to an exterior wall. I have removed all venting and there was some residue but nothing major which was cleaned out. I also cleaned all of the burners using about 120 psi air pressure. I did remove all the burners when I cleaned them and had no idea that there was any difference in them. I thought that they were all identical so if I did not put them back in the proper order that may be the reason that I am having the code 12 problem. Is there any way that I can see and determine which burner goes where by simply looking at the burners?

Jack

The burners are identical. When you consider, over time, the number of firings on low vs high fire plus whatever residue might accumulate in the HX, as you found, it is likely that a small amount of that residue could end up on the burner and possibly cause a slight warp age due to a hot spot. It isn’t common, but does happen. Is the vent graded to the outside?

Jack

Also, you “ don’t think” there is a gas pressure problem, but with all you have replaced I think you need to see the high and low pressure setting on the unit while operating.

agt

The vent is mostly graded to the outside. The local installer did a pretty poor job of installing the vent as of the 14' of the vent about half of it was vented to the outside and the other half was vented to the heater which is reason for some condensation having gone back into the heater. After cleaning the vent, I realigned the vent to vent out from the 90 elbow for about 75% of the length. I will need to redo the exit through the wall so as to have the entire length graded to the outside. The current clearing from the vent to the exterior soil is currently 14.5", would it be a problem if I lowered it to say 12"?

As far as my burners are concerned should I try to rearrange them so as to get a better overall flame pattern?

agt

You are probably right about the gas pressure, so before I give up on this 11 year old R53i, I will get in touch with a gas fitter that I trust and will have do a low and high pressure check on it. If I decide to replace it I am thinking of the R75i, would that be a good choice for 2 to 4 people?

agt

One more thing that I should have mentioned about our hot water problem is that on some occasions, we get a pulsation of the water flow when getting hot water at a low flow level. Not sure if that is connected to our overall problem with getting hot water but thought I should have mentioned it.
I will have checked the low and high gas pressures early next week and will let you know what the results were.

Jack

The 12” is the minimum but ok, depending upon snow levels. Having issues with pulsating flow at low flow conditions means you may be falling below the .25 gpm lower threshold for operation. What temp are you running the unit. Perhaps you should turn the temp down to increase the hot mix to arrive at use temp. If over the years you have had condensation on the HX, that moisture boils off and leaves the precipitation in the fins of the coil. That condition is very hard...very hard to clean. Ultimately that will lead to hot spots and HX failure. If the unit vent cannot be properly graded you are wasting your money doing the repair. The RL75 is the correct replacement for the 53. I have the 75 at home. Now, Having worked with Rinnai for 27 yrs I am exceedingly biased, but I no longer have any business affiliation with them. That said, if I was buying a new tankless today, I would only buy the new Sensei unit. The 75 will handle your load but the RU 160 would have about identical capacity and is impervious to condensate. Larger capacity units are available. I favor the Sensei for a reason which you will surely understand given the amount of time you have been in a close cuddle with the 53. The HX is SS and you can have the entire unit torn down in less than 10 min. Service time is a major issue in any industry.

agt

If after checking and adjusting the high and low gas pressures, I still have a problem, I will then give up on the R53i and proceed with purchasing the RU160iN as per your suggestion. I see from the information on this unit that i would be able to use my existing concentric venting which I would not have to worry about it's existing grading. Will let you know how things are going after i have checked the gas pressures.

Jack

Sorry, but, No, the venting will have to be changed. Your current venting for the .82EF unit has a heavy AL liner. The RU unit is .95EF and requires the polypropylene 2/4" concentric. The pH on the condensate is about 3.2 which makes it pretty hot and it would eat that AL in short order. The RU unit would also require a drain for the condensate.

agt

In that case it probably would be cheaper for me to use the 2" dual pipe venting?

Jack

Your dollars, your choice. I strongly recommend that you keep it a direct vent.

agt

Gas setting procedure for my R53i requires a minimum of 3 gallons of water flowing through the heater in order for me to adjust the low and high gas pressures. Unfortunately, I can barely run one gallon per minute through the water heater so as to keep the burners going. Anything more simply shuts the heater off and produces a code 12.
As a result, I don't see how it is possible to do any adjustments on the gas valve.
Does this mean that the gas valve is faulty?

agt

Using manometer UEi EM152 and inH20 scale, I get a reading of between 1.45 and 1.50 in forced low measurement with dip switch 7 set at ON in SW1 no matter how much I adjust the regulator screw of the modulating valve in or out and I get basically get the same measurement when I attempt to adjust the forced high and set the dip switches 7 and 8 to ON and again no difference when turning the potentiometer fully clockwise or counterclockwise.
The lack of any change when doing adjustments is probably connected to the low amount of water running through the water heater but does this situation point to where the problem might be?

agt

My gas inlet gas pressure is 2.65 inH20 to my water heater gas valve at the bottom of the unit and I understand that it should be min 6.0 wc and max 10.5 wc and for adjustments min 7.0 wc. Looks like I probably should contact my gas utility to come and check their meter and regulator. Please let me know if I am still missing something or if you agree that I should contact my gas supply utility to check their meter and regulator.

agt

As a follow up to my last comment, is it possible that there could be a leak within my gas valve system that would affect my low 2.65 reading at the inlet connection to my valve? I took the measurement while the gas heater was not operational.

Jack

Sorry, but I do not have the settings at hand, but if you have very low inlet pressure, it is difficult for the unit to do its thing. Do call the utility to check things out.

agt

I plan on calling my utility tomorrow but I will first check my gas pressure at the 3/4" cap below the gas valve that connects to my gas heater and from there connects directly to the 1 1/4" line that connects to my gas meter.

agt

I checked my gas pressure at the meter source and I was still getting 2.79 in H20 so I contacted my gas supplier and they checked the gas pressure and it measured at 7.45 in H20. My manometer is the UEi model EM152 which is supposed to be pretty good quality. After the departure of my gas supplier gas tech, I rechecked my inlet gas pressure with my manometer and it measured 5.05 from the left port and 2.79 from the right port so that pretty well confirmed that the tester is faulty. I have a replacement on order and will once again try to adjust my low and high fire adjustments on my R53i and take it from there.

agt

Hi Jack, I tested the inlet gas pressure with my new gas tester and I am getting 7.25 inh20 which is basically the same as what my gas utility tech was getting when he tested it last week so now I know that my tester is working properly. I then proceeded to try to adjust my low and high fire gas settings and adjusting both the forced low setting with dip switch 7 set to ON (supposed to get 0.77 but getting 2.5) which did not make any difference when turning the regulator screw on the bottom of the modulating valve and no difference either when trying to adjust the Potentiometer when trying to adjust the forced high with both dip switch 7 and 8 set to ON (supposed to get 3.77 but getting 2.5). The reading I get with both dip switches 7 and 8 set to OFF is 4.0 inh20. This may have something to do with the fact that I cannot run more than 1 gal of water per minute or else the burner shuts off and I get a code 12.
If I knew for sure that this is a gas valve problem, I would order one and replace it but otherwise I think as you suggested that I should give up on trying to fix it and purchase a new one.
I will wait for your final thoughts on this matter before making a final decision. Thanks

agt

Jack, after going over your comments I came across your question as to the condition of the HX and realized that I forgot to mention that the unit was installed in 2007 and was cleaned by the original owner once and as far as I know was never cleaned again until just a month ago when I purged it twice with 4 gallons of vinegar. Is it possible that there is some large chunks of calcium inside the heat exchanger that were not cleaned out and are preventing proper flow of water through it thereby causing the Code 12?