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Old 06-07-2020, 08:56 PM   #1
Junior Member
Brand: Thor Motor Coach
Model: Gemini TX
State: Ontario
Posts: 27
THOR #13247
12v Marine Pump Not Strong Enough for Hotwater - No Leaks

2017 Thor Gemini TX

12v pump not strong enough to hold pressure more than 5 seconds to run
tankless hotwater while boondocking.

Hotwater works great and good pressure with City Connection from hose bib.

This solely a 12volt marine pump issue.

Done rough diagnostics so far.

- 12volt Shur-flo 3 gal per minute OEM pump from Thor.

- Pump screen is cleaned and clear.

- No Leaks Pumps will cycle on and off. Will shut off in 20 seconds when system is pressurized.

- During this brief period the electronic hotwater control will light up and work (spinning wheel for activation) for the 5 or so seconds and then shut off as pressure drops.

- Out of Water tank is 1/2 PEX Piping

- Has anyone solved this Hotwater turning on briefly then off when pressure drops by;

- Increasing the pump sizing.

- Increased the water intake to the Shur-flow Marine pump from 1/2 to 3/4" PEX piping from Water Tank to Pump Intake as to not restrict water into the pump.

Been like this from almost the start.

Thank you for your help

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Old 06-07-2020, 09:53 PM   #2
Senior Member
Brand: Thor Motor Coach
State: Ontario
Posts: 251
THOR #13224
Look on youtube and there is a description of how to increase the pressure with an allen key. You can also call Shurflo tech support and they are very good at walking you through it also. Been there.

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Old 06-08-2020, 09:38 PM   #3
Junior Member
Brand: Thor Motor Coach
Model: Gemini TX
State: Ontario
Posts: 27
THOR #13247
Problem Solved:

Pump being a little older and being stored in winter in the Northeast is not as strong as it is of course as new.

Pressure adjustment on the pump itself only works so far.

Turn allen key screw clockwise to boost pressure, however once tap or device is used pressure will drop and Hotwater will still shut off let alone the tweaking between pump cycling on and not cycling off.

This is all about water throughput from tank to pump to hotwater supply.

An allen key is required on the center of the pump flange or pressure sensor.

Removed as many flow restriction from tank to pump to hotwater supply.

- Remove 90 deg elbows off the pump

-Remove tank water shutoff and put in a flow thru PEX ball valve and not OEM Thor shut off that restricts water flow.

I am going to replace piping from tank to water pump filter with 3/4 PEX from 1/2" PEX to reduce resistance to the pump.

This would have been the best solution in my estimate and the use of 45 deg fittings only if absolutely necessary.

Of course a stronger pump would have compensated for the fact this pump in its age with the water restriction is sized perfectly and when pump becomes older, may require modifications at the pump inlet side or outlet to the devices to maximum flow from the pump.

As doing all this, not that difficult the pump is working fine and the pump will as a result be working more efficiently.

Another Thor improvement over factory install.
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clarkwood is offline   Reply With Quote
Old 06-09-2020, 02:48 AM   #4
Senior Member
Judge's Avatar
Brand: Thor Motor Coach
Model: 2020 Magnitude SV34
State: Florida
Posts: 1,398
THOR #12751
I've had two coaches now with the tankless water heater and now and never had an issue with pump proving enough flow. Of course when showing I never mix cold water or turn on the water anywhere else in the coach.

The only time I have heard my pump cycling is when the tank is empty and it is sucking air.

Any chance you have a minor leak with the check-valve? Perhaps a small leak where some water is going out the city water inlet?

My 2018 Outlaw 29H had some flow issues and I discovered it was construction debris in the plumbing that built up in the water restrictions at each faucet.
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