The rinnai 20 Infinity is perfect but have recently noted a problem. I found the basin hot water tap in the bathroom begin dripping only when the kitchen hot water tap is turned on. I don't know how long this has been going on as it was by chance that someone turned on the kitchen tap while I was in the bathroom. It obviously appears to be a pressure problem, but what? Peter

trouble shooting section will help https://sahotwater.com.au/specifications/Rinnai/Service%20manual/smV1616W_V2018W_V2020W.pdf

If it is hot in the kitchen, then once the water has reached the shower it should be hot. The leads me to believe that the issue is with your shower mixer unit. Nearly all are thermostatically controlled.

Or, if the heater is downstairs and the bathroom is upstairs, you don't have enough hot water pressure. You need a good plumber with a pressure tester (called a manometer).

When is the last time it was flushed?

The hot side of the faucet is most likely plugged with something that came up thru the water system. The average thankless waterheater requires at least 1/2 to 3/4 gpm flow rate for the unit to sense flow and turn on. If there is not enough flow it will not fire and heat the water. Not sure about this particular unit but a few require at least one full gallon per minute flow. So chances are that if you fix the faucet, you fix the hot water issue at the same time

Sounds like the diaphram in the gas control valve which is not replacable. You would have to replace the gas control valve and I would also suggest replacing the thermocouple. However since the heater is 8 years old you may think about replacing the entire hot water heater. Depending on how much water has gone through it in these past 8 years it will probably rust out soon and then you will be dealing with a flood.

Good luck,

Marty

Ask the plumber who did the mods. to come a check that he hasn't crossed a hot/cold pipe. Really sounds like he has, this would cause hot water to mix with cold. Is the water hotter further away from where he did his work? This would be a clue. Easy way to check is to turn off the water to the hot water system, should be a valve on the middle pipe going in to the heater. This should turn off all water to all your hot taps. If you still have water at any hot tap or shower then the pipes have been crossed.

Run through the basic checks

• Power lead from the heater plugged in a socket turned on.
• Gas on to house
• All valves below heater in on position.
• If they have controllers in the house turn on (key pads marked with Rinnai logo in kitchen or bathrooms usually)

There is a turbine that spins in the heater when a hot tap is run. If the heater has been sat for some time not operating the turbine might have stuck. Run the hot tap and keep it running, using a hammer give the centre pipe connection under the heater a firm hit a few times(not too hard). This might unstick the turbine.

Usually this type of fault is down to poor water flow. Basically you are asking the unit to work at a level below it's minimum output. Easy thing to try is to check any filters or water flow limiters in your tapware. Usually these are in the nozzle of the tap. I often take these out. The inifinty reduces water flow anyway and there is no reason to have water limiters. Try turning on two taps at once. If this stops the fault then you definately need to increase your water flow. Make sure the mains water is turned on full. Aslo you can check the cold water filter on the infinity. It's just above the cold water isolation tap (middle pipe as you look at it), turn that off first, the filter is a round plastic nut, unscreww it and clean the filter. Reconnect, turn you mains water back on.
There are other faults but this is by far the most common.

Just joined fixya and am a Rinnai service manager in Australia. Is this still an issue?

you can get it off the rinnai web site they have a spot on there to get the internet manuel,, but from what you are saying you may need to adjust the thermostat, or the temp, remember even though you will have endless hot water it still takes the smae amount of timed for the hot water to get to your faucet,, not only that make sure your shower heads aren't holding back to much water pressure, if you don't have enough water going thru the unit it will not stay lit, if will come on and go off, judt to dstisfy the unit,, make sure the filter is clear, on the cold side there is a cap screw if you take it off there is a screen in side you just pull it out and clean it and reinstal it,,