This unit is 4 years old and has run perfectly until recently. It ignites ok and the pilot stays lit and the burner will light all the way but when the unit goes to high fire it shuts down and tries to ignite again. This problem is sporadic - sometimes its fine for a couple of days and then it just decides to quit. Water is town water on a softener. Unit is clean throughout and water valve filter is clean. Exhaust has no obstructions and blower is working fine. Unit will sometimes shut down after a few minutes of use and then reignite after water is tuned off and then on again. The heat exchanger is clean and free from dust buildup.
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Call a qualified service tech immediately. Gas explosion indicates dirty combustion parts, and gas is not fully igniting when tankless turns on the gas. So gas builds up and then explodes causing serious damage to tankless, and serious risk to homeowner.
im leaning towards the thermocoupler its like a eye only it measures the heat at the pilot tight if it tells the unit its off it shuts down and turnes the gas off thats why you have to keep relighting hope this helps.
I have the same problem with the same model. The problem has been identified by a friend of mine, correctly, I think.
This is a very dangerous problem involving Bosch's much touted safety feature, ironically enough. IT IS THE FLAME SENSOR IN THE GAS VALVE. The flame sensor is supposed to confirm that the pilot has lighted BEFORE the main gas line sends gas to the main burners, after which the pilot shuts off. The pilot light is not coming on, the sensor that shouldn't let gas fto the main burners is failing and the main gas is flowing and ignighting from the spark that is supposed to light only the pilot in a big explosion.
This is the 2nd unit of this model that has failed. I think Bosch should do a recall
It's the gas valve. This pretty common. The thermocouple produces a small amount of current from the heat and this current holds the safety valve open inside the gas valve. Sometimes the safety valve gets sticky and your symptoms describe it exactly. People are always frustrated by the time it is certain to be the valve. You need to replace the valve. No one is allowed to fix a gas valve - liability - gas etc. Replace the gas valve and your problem will be solved. I am a master plumber/gasfitter and I am confident that this will solve the problem. Been there - done that.
The manual says to hold a match near the pilot while the ignitor is
trying. It says that if the unit lights the pilot orifice may be dirty
or clogged. Then the manual says to check
the voltage on the igniter. It should be 1.3 volts DC minimum if it is not means the electronic control box is defective.
The clicking is a good sign. What are you trying that not working? How is the water flow-is it strong? 1) Turn the flow control button all the way to your left - this will increase the flow.
2) Pull the relief valve to simulate water flow and listen for clicking sound, and hopefully, main burner ignition. ( if installed in basement or kindly use bucket to catch water) The 1600 H NG will automatically shut off firing after 5sec of clicking.
3) How is the venting-use a household digital carbon monoxoide detector to measure any backspill from chimney.
4) Was the gas line disconnected in anyway after heater was installed? Air in the gas line will cause the igniter to click but no gas to fired the main burner.
Todate i have installed 11 Bosch Tankless Heaters -- 9(125 NG) Which is the same as 1600 Series
1(1600H NG) and 1(1600P NG)
Guess which one I having problem with- You guess it, however, the problem is their electrical wiring.
BE CAREFUL IN CALLNG BOSCH TECH. FOR SUPPORT. THE ARE GRILLING YOU TO FIND A LOOPHOLE WITH YOUR INSTALLATION TO RELIEF THEMSELF OF THEIR WARRANTY.
It is most likely the water valve stuck open, telling the controls to heat water, that it thinks is flowing through it, but without actual flow it overheats. Depending on how comfortable you are with taking it apart yourself, you could open the valve to see if it just needs cleaned out, or if you have a ruptured diaphragm or some other cause.