Shower temperature fluctuating and will not stabilise

Fiats have a reputation for electrical/electronic problems as they age and even when they are not very old they can manage strange things that even sometimes defeat the dealers, though the same can be said of many modern vehicles. I used to look after a Ducato motorhome and fortunately didn't need to get involved with much electrical work - the only faults were caused by the coachbuilders rushing around and being careless and not by Fiat.

I am not sure if the temp gauge is driven by the engine management or is a traditional circuit but either way the temperature gauge is in effect a voltmeter of sorts. Assuming the gauge is ok, the reading will only fluctuate if the voltage in the circuit fluctuates and that could mean the supply voltage is fluctuating or the resistance of the ground path is fluctuating.

With the traditional circuit the gauge is supplied by an electronically stabilised voltage and the ground path resistance is varied by the engine coolant temperature sensor and fluctuations could be anything from a faulty instrument voltage regulator, through faulty wiring or connections to the temperature actually fluctuating.

If the gauge is driven by the engine management the same approximately applies but checking the circuit becomes much more complex due to the need for circuit diagrams and specialised test equipment, though these would not be needed just to check the security of the gauge in the printed circuit of the instrument panel.

i am not an expert but i have a hunch it could be the tempeture gauge but i have no solution sory

if you are living in an appartment water temperature can fluctuate if the construction plummer has linked some appartments with the same provider (water company) and so when your neighbour turns on his sink to the hot water he lowers the pressure so you get less hot water and the same cold. All that results in when your neighbour turns the hot on you get colder water and when he turns cold on you get hotter water.

1. COLD MIX, HEATER DEACTIVATES
   If inlet water temperature is over 70°F due to geographic location, water maybe very hot out of the tap. This requires a lot of cold water to be added with it in order to attain a useable hot water temperature. The addition of too much cold water will overpower hot water demand from the tankless water heater. This slows the flow within the tankless water heater, decreasing it below activation point, which shuts off the heater. The end result is nothing but cold water coming out of the outlet. See: TWH E2-04 Overcoming fluctuating temperatures [PDF].
2. FLUCTUATING WATER PRESSURE
   If the water pressure in the home is erratic and the water flow is not consistent while a tap is opened, then the temperature of hot water will fluctuate. The minimum water pressure for the home should be 30psi or greater. For people on well systems the minimum pressure range is 30-50psi. The use of a pressure reducing/regulating valve is an effective way to maintain constant water pressure to the water heater. Watts brand 25AUB- ¾" or N35B-¾" pressure reducing/regulating valves or equivalent is suggested.
3. CHANGING FLOW RATE
   Major changes in flow rate can adversely affect the output water temperature of the heater. Increases from one major fixture running to multiple fixtures running at one time can cause the temperature to fluctuate. Stay within the heater's specifications. See: TWH E2-03 Outlet temperature vs. flow rate [PDF].

From the Bosch website.

Good Luck,
Gary

Test: take the shower head off, then run water. If the water can be adjusted to the desired level (hot/cold mix), then the problem is probably in the shower head. Contact the manufacturer of the shower head. If you cannot maintain a good mix, the problem may be in the valve behind the wall or a total house pressure problem---time to get out your wallet and call a plumber.

Iam guessing your using it faster than it makes hot water. May need a larger unit or a second one,in the system

This is a great heater. It is however crucial that it be installed to every detail of the manual. If there is trouble send pictures to Bosch tankless you can call 1-800-283-3787 ask for Bosch Tech support or go to boschhotwater.com click find a contractor and call the closest Bosch Service Provider most will travel.

Sounds like there is not enough flow in order to keep the burner in the heater firing continuously

hi there! there is a technical problem in concern with that for sure...try checking the handle it might be loose already. things like that do happened all the time. thanks, kindly rate.

Yes this one for the pro's call the company this is not something a most repair plumbers like to do...we would call the company they should know whats going on. If I was on the job thats what I would have to do, and then I would have them ship the parts to me. How old is it?