Question about Bosch AquaStar 125FXKIT-NG 125FX Natural Gas Tankless Water Heater w/ Hood

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Bosch 16p gas, keeps going hot and cold

I have a bosch 16p which is about 8 years old.....for some reason it heats up for a few seconds the goes cold, i can not get constant hot water. any suggestions? easier just to call a plumber? do i need a new system?

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As Duncan Vu suggested, its probably your diaphragm. The quality of them seems to have gone down hill in the past 10 or so years and you will probably get about 3 years out of them before they wear through. Piece of cake to change out. 1. TURN OFF THE GAS, 2. Turn Off The Water. 3. Disconnect the water pipes from the Diaphragm housing (don't lose the washers). 4 Two philips head screws lock the top of the diaphragm housing into the gas housing, loosen these and the diaphragm housing will drop out. 5. You can now carefully hold the diaphragm housing in a vice and undo the three large philips head screws that hold the diaphragm cover on, lift it off, pull out the old diaphragm and put in a new one. reverse the steps to get it back together and you should have constant hot water again for another few years. Please note this is just a rough guide and if the steps seem in any way difficult or not obvious don't try it. I'm not responsible for any damage you do to you or your house or yourself if you screw it up....

Posted on Mar 19, 2014

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I had the exact same problem, I called Bosch and they gave me a local contact (hot water repairer). I spoke to him and told him the problem and he identified the likely caused over the phone, he attended and replaced the diaphragm in the regulator - all fixed and back to normal endless HOT water.

Posted on Jun 25, 2013

  • Duncan Vu Jun 25, 2013

    I had the exact same problem, I called Bosch and they gave me a local contact (hot water repairer). I spoke to him and told him the problem and he identified the likely caused over the phone, he attended and replaced the diaphragm in the regulator - all fixed and back to normal endless HOT water.

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Check the thermostat, you will probly need someone that has worked on the same kind of unit, they are not all the same {tankless} I would suggest a repairman,, there is a little bit much to explain how to do it over the internet,

Posted on Jun 23, 2009

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