Why is my D5 Solar Hot Water Pump Losing Pressure?

Paul had a problem with his D5 solar hot water pump losing pressure, or so he thought at first. Here’s what happened…

Here’s the Issue…

Paul (Customer) writes:

I am using the D5 solar hot water pump on a solar heated hot tub.

It worked perfectly last winter and I could heat the tub well above 105 degrees but late this summer the tub seemed to have trouble heating to 101 degrees.

Since we have monsoons mid-July through mid-September with cloulds a portion of every day I assumed it was lack of full sun. Now that we have full sun all day I discovered the pump works sporadically. I have a value before the pump to insure the water level in the tub is above the level of the pump.

I have a second valve about two feet beyond the pump and about 14 inches higher than the pump. The purpose of this value is to insure the pump is working and producing a good stream of water.

Not Enough Pressure

On some days when the pump is receiving power I do not get water pumped to the second value. I am sure the pump is primed. I can unplug the pump and plug it back in and it will being working but produces a weak stream of water at the second value.

There is not enough pressure to pump eight feet of head to the top of the hot water panels.

Lately the pump sometimes makes a rattling noise and sometimes it does not sound as if it is operating. Nor can I feel any slight vibration to indicate the impeller is turning.

I opened the pump on one occasion when it was not pumping and confirmed there was no debris in the pump and that the impeller spun freely.

I did not find any problems.

When I reassembled and reinstalled the pump it worked flawlessly for two or three days before returning to working sporadically.

Any thoughts?

A Good Test to Run

Mike Kehoe:

Have you adjusted the speed dial on the bottom of the pump?

What is the wattage of the solar panel?

That can affect the way the pump works. Especially if the speed is set above the wattage the solar panel is putting out.

A good test is to run the pump directly from a car battery. If it runs properly then you know the problem is elsewhere. Because a car battery is putting out straight 12V with more than adequate amperage and wattage.

It Might Be the Power Supply?

Paul writes:

Thanks for your quick responses. Makes me more than willing to recommend US Solar Pumps.

I have a dedicated 12-volt supply plugged into 120 volts AC which is controlled by a differential temperature controller.

This morning it occurred to me that it might be the power supply which I have not tested since the problems began.

I think I will confirm the output of the power supply and then replace it for a few days with a 12-volt deep cycle battery to see if it makes a difference.

Hopefully, the problem is the power supply which is the easiest and least expensive solution.

Thanks for your help.

Mike Kehoe:

Please keep me posted. Mike

Conclusion – Why the D5 Solar Hot Water Pump is Losing Pressure in my Drain Back System

Paul writes:

I have the problem resolved! Found out why the pump was losing pressure.

My hot tub is a drain back system, so I had installed a vacuum breaker at the top of the hot water panels to allow the system to drain and prevent freezing.

From the beginning the system worked well and would pump the air out of the panels and into the hot tub.

About two weeks ago I removed the vacuum breaker and installed a vertical pipe about 20 inches long with an elbow at the top.

This allows the system to drain at night but also allows the air in the panels to exit so the pump does not have to force it all the way through the system back to the hot tub.

Since removing the vacuum breaker and installing the pipe the system has worked flawlessly. The pump is doing well. Now the pump is not losing pressure.

Thanks again for your quick responses.

Feel free to contact US Solar Pumps if you have any questions about your pump losing pressure! We would be happy to help. Our WhatsApp number is: 1-570-780-9524