We have a Rinnai natural gas water heater. Earlier this evening, while my daughter was in the shower, the hot water stopped. It came back on a while later, but then when I was in the shower, it stopped again, and hasn't come back on. We are having extreme cold temperatures (around -10) right now, so I don't know if that has anything to do with it, but nothing seems amiss when I check it out. Of course, I don't really know what to look for.
Could be the water supply into the heater after the cold supply to the house has frozen up. Sounds like an ice block has moved down the pipe before the heater while the water to the shower was flowing and then got lodged in an elbow blocking the flow.
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Contact Rinnai. Gas control valve is different, burner is different, burner and gas valve must match, threads are regular instead of reverse, dip switches probably have to be changed since combustion of NG is not as hot. Maybe different sensors. Pressures are lower with NG.
Try running the hot water in the sink while you have the shower. If the water in the shower stays hot, then the problem is not enough flow through the water heater to keep the heater running. I am guessing that the master bath is further away from the water heater than the guest bath. If not I would check the shower nozzle in the master bath to see if it is clogged a bit or if it is a water saver nozzle because this will slow down the water volume and then cause the water heater to shut off the heat.
A fault often found with these units is due to insufficient water flow. Usually this causes specifically the shower to run hot and cold. Try turning on more than one hot supply; if this fixxes the fault you will need to try and increase water flow. Most new tapware/showerware have water flow restictors built in. These are the cause of many problems with continous flow heaters such as the Rinnai. In taps they are usually located in the spout if it unscrews. In showers try the shower hose. Find them and take them out. Also make sure your mains supply to the house is on full.
There are more technical faults but this is something you can easily try first.
this is usually a problem with all tankless water heaters.
the solution is to install a small buffer tank (5 or 10 gallon electric water heater) after the Rinnai. this will give the water something to mix in. it will solve your problem.
did you make sure to use a 3/4" gas line to the unit. not just 3/4" at the unit itself. sometimes when there is not enough gas, the unit will act funny and cycle from hot to warm or even cold. Make sure you check the gas line size, its very important.
If you aren't getting any error codes, then the heater is probably doing its job. Your problem is probably somewhere in your plumbing system. The most common reason you get this sort of problem is due to cold water mixing in the hot water system. There are a number of causes for a "cross connection" :
-Faulty check valve -Missing check valve on reciculation return line -Faulty shower cartridge -Thermostatic mixing valve set too low -Faulty thermostatic mixing valve -Faulty anti-scald valve
The easiest way to confirm a cross connection is to: 1) shutoff the cold water entering the tankless heater 2) open hot water valves around the house. If you still have water flowing at your hot water fixtures, then you have a cross connection.
did you size the gas line properly? sometimes if the gas pipe isn't sized properly it will cause some pretty loud wistling noises. also if you have something in the fan like bugs or lots of dust it will cause alot of problems with noises
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,,
Try this before replacing the shower diverter valve.
If this problem is isolated to the shower only, then I would suggest that the shower diverter valve is equipped with an "Anti-scald" safety feature that can not be adjusted, however the temperature regulator/thermostat on the water heater can be adjusted to a lower temperature so as to not activate the the "Anti-scald".