Off Grid Home Forums Technical Discussion Problem with 12 v pump supplying on demand water heater

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    I have a 12 volt Sureflow on demand pump supplying a Bosch on demand propane water heater. Pump turns on and off every couple of seconds when hot tap is on. Cold system works fine.

    I think back pressure in heater signals pump to turn off. Would a pressure tank or an expansion tank in the system solve the problem?

    Is a larger pump required?

    Pump turns on at 25 and off at 40 psi.


    We have a similar setup, and yes, we have a pressure tank, otherwise, every time we run the water the pump comes on, this is much quieter and makes the water pressure more even.


    Nick Rosen

    Yes, you need a pressure tank. I have a little 2 gallon one I ordered from backwoods solar in Idaho that works great & will make your pump last longer


    At one time I worked for an RV place and we saw all sorts of ‘defective’ shureflo pumps. I discovered I could disable the ‘defective’ pressure switch by replacing it with a blanking plate and some silicon gasket goo.

    Naturally the customer got a replacement pump and went away happy but I saw no reason to throw away perfectly good pumps that just had a problem with a pressure switch. Sometimes I could even fix the faulty switch by adjusting it. You could also plumb in an external pressure switch. Some systems use a pump requiring an external switch so get one of those and bypass the Shurflo switch.

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