Rinnai R94LS (Propane) no longer getting very hot

chester123

My Rinnai 94LS (propane) has been supplying domestic hot water and auxiliary heat to our heat pump for ~10 years. Because of the auxiliary heat loop it was set to 185 in the winter and mixed down for domestic. Over time I have had to increase the mix and now it's "full open". With the unit set to 160 I can get about 110 degrees at domestic points. This happened gradually over the last five years. In other words, the max heat temp has been reducing from 160+ down to 110 over time.

I flushed it once a year with vinegar and have cleaned the filter screen. The fan sounds good (i.e., no loudness or irregular sounds like it's out of balance). The stack seems clear and there are no error codes.

Any suggestions? Maybe the heat exchanger has been clogging over time? I thought I should check in before I replace it though. I'm reasonably savvy and can do stuff if you can point me in the right direction.

Derheatmeister

chester123 said:

My Rinnai 94LS (propane) has been supplying domestic hot water and auxiliary heat to our heat pump for ~10 years. Because of the auxiliary heat loop it was set to 185 in the winter and mixed down for domestic. Over time I have had to increase the mix and now it's "full open". With the unit set to 160 I can get about 110 degrees at domestic points. This happened gradually over the last five years. In other words, the max heat temp has been reducing from 160+ down to 110 over time.

I flushed it once a year with vinegar and have cleaned the filter screen. The fan sounds good (i.e., no loudness or irregular sounds like it's out of balance). The stack seems clear and there are no error codes.

Any suggestions? Maybe the heat exchanger has been clogging over time? I thought I should check in before I replace it though. I'm reasonably savvy and can do stuff if you can point me in the right direction.

Are you on a Well ? Maybe using something like Fernox DS 40 with a "Pony pump" will help.

chester123

We are not on well water, but I do have a pump and could try the Fernox. It looks fancy! Is the idea that it will clean the heat exchanger better than the vinegar?

Last time I used the vinegar it ran pretty clear and eventually turned blueish, I assume from reacting with the copper.

rick in Alaska

I would pull it apart and clean the heat exchanger. It can get various bugs and other small flying critters into that area and plug up the holes in the exchanger. Also clean out the fan while you have it apart, as I have had moths get packed in there which will cause severe vibrations if not cleaned out.
Also check out the incoming water turbine to make sure it is not sticking.
Rick

Jamie Hall

While you are at it, clean the mixing valve. You don't specify, but I have to wonder if the problem is a sticking mixing valve, or out of calibration, rather than in the boiler...

chester123

OK. I'll clean all the stuff (looking for YouTube videos). The mixing valve is a very interesting idea. It still changes the temperature at the faucet when I adjust it, but I can see how that wouldn't guarantee that things are working properly. Let me see if I can get in there.

Thanks for the suggestions!

chester123

FYI: Things look pretty good (clean, bug and dust free) on the outside of the innards.

rick in Alaska

Those parts always look clean. What needs to happen to properly clean it is to remove the blower fan. Then the heat exchanger, which is behind the plates with VAFF and LPG written on it. It takes a bit, but to properly do it it needs to be disassembled.
Rick

chester123

Sounds good!

chester123

Well, hopefully people are checking the board on a Saturday

I have everything apart. The fan looked reasonably good, but I brushed and vacuumed/blew it out anyway. I have the burner out and will brush it as best as I can. I only have access to the bottom of the heat exchanger in my current state of disassembly. But from what I can see it looks like it could use a good brushing as well. Any suggestions for how to access the whole thing? Could I pull it out and soak it in something? Thanks!

chester123

Actually, I'm feeling pretty good about the heat exchanger. I can't easily do anything about the copper oxidation, but I blew it out / vacuumed it out pretty good and lots of nastiness came out--in particular lots of what appeared to be drywall dust. It's looking reasonably good now. Put it back together?

Larry Weingarten

Hi, Is there any way to have a look inside of the coils, just to make sure there is no scale built up there?

Yours, Larry

chester123

Not that I can think of. I ordered some heavier duty flush (than my usual vinegar) and will try that.

I just put everything back together. Went together fine, no codes. Water temperatures are exactly the same. Regardless of the setting at the heater (i.e., 120, 125, 140, 160, 185) the temperature at the nearest faucet is 102.

Thermostatic mixing valve is full open. Cold water temp is 49. Except for the new flush I'm out of ideas.

<< edit >> I'm going to check the output water temperature right at the machine.

chester123

That was it! It's the mixing valve. Temperature straight out of the heater = very hot.

In retrospect this makes all of the sense in the world: It's a thermostatic valve, so of course the temperature was consistent at the faucet regardless of the setting at the heater.

It's a pretty expensive valve ($250!) so I'm bummed it failed. But good to know what the problem is! And, on the plus side, I have a fully tuned-up heater now! Thanks for all of the help.

chester123

OK. I tried rebuilding the valve, but to no avail. The problem persists! So I'm going to buy a new one. The existing valve was soldered into place (lame) but I'd like to change the fittings to make future maintenance easier.

Any recommendations for a valve? I'm currently looking at: https://customer.resideo.com/en-US/Pages/Product.aspx?cat=HonECC%20Catalog&amp;pid=AM101-US-1LF/U

hot_rod

Flow test the heater with a bucket, stop watch and temperature gauge to be sure it is performing

I’d run a product like Hercules Sizzle through the HX. Make sure any other product you consider is listed for potable water use, not all descalers are.

If you want to replace the mix valve look for a quick responding version. The Caleffi 520 was built specifically for tankless coils and tankless heaters. It also has 100% shutdown should the cold side fail, scald guard function.

Slimpickins

The simple thing to check is to make sure you don't have a crossover connection. To check for that, put a hose on the service drain on the hot outlet side, shut the cold supply ball valve off and open the hose. if you have flow, you have a cross. To prove that, next close the ball valve on the hot outlet and open the cold supply ball valve and run water out the hose on the hot service drain and if you have 160 degree water, that's your problem. This happens a lot commercially with sprayers, mop sinks and check valves. If that's not it could be a water flow control valve (servo) that is allowing too much water through the unit of the bypass could be faulty and mixing too much cold water to the hot water outlet. Other things could be the high fire gas solenoid not engaging or it could be a gas valve.

Rinnai has great tech support, I'd give them a call if its not a cross and they will help you out. Make sure you have the model and serial number along with your multimeter and manometer ready. That unit is nearing the end of it's life, especially running at those high temps and a lot of parts are becoming not available. Might be best to replace with another Rinnai non-condensing model because you could use the same venting if it's in good shape.