Heater: How do I know if the problem is the water pressure vs the pressure switch?

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A

aasarava

0
Dec 28, 2015
32
San Diego, CA
Hi, I have Minimax 400 pool & spa heater that stopped working this weekend. Though the power light was coming on, the pressure light was not. So I removed the rusty pressure switch and jumped the wires with a paperclip. Sure enough, the heater starts up now. But how can I be sure the issue is just the pressure switch, and not actually with the water pressure? If the spa water heats up, does that mean the pressure is fine and I just need to replace the switch?

Thanks!
 
Clean your filter and see what happens. If you have a cartridge filter you can remove the cartridge from the filter housing and then see what happens with the heater.
 
Thanks for the tips!

Paul -- The filter had just been cleaned a couple weeks earlier, so there's not much chance it's the filter. All other pool functions are running fine.

kadavis -- That's interesting. I finally got the pressure switch off. (It was so corroded that it snapped off.) There was a little water and air that came out, but I wouldn't call it a steady stream of water. Note that the system was completely off, though.

Anyway, since the pressure switch snapped off, I ordered another one. Once I get that on, we'll see if everything runs as expected. If not, then I'll have to investigate a potential clog in the line.

Thanks!
 
What I will do on some units, making sure to protect the electronic components, once I remove the pressure switch, I will turn the pump on and let is flush the line. Just make sure you kill the power to the heater!
 
Thanks for the tips, guys. I ended up replacing the switch with a Pentair 470190Z switch, which has a plastic body and is less likely to corrode than the original. (The original was a Barksdale MSPS-EE05-Q11.)

It took me a while to find the right adapter fitting. Turns out that since the new switch has plastic threads, I needed to replace the little brass fitting with a plastic fitting. In case anyone's trying to do the same thing, the new fitting has a push-in end for 1/4" copper tubing, and a threaded male end for 1/4" plastic threads.

Photo: Imgur: The most awesome images on the Internet

I didn't see Paul's message about flushing the line (good idea) until after I installed it. But everything seems to work and the spa is back in action, so I think the problem really was the switch.

Hope this helps others in the same situation. Thanks!
 
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I spoke too soon. Grrrrr. While the heater now turns on and the pressure light stays lit, the heater is now short cycling -- i.e., heating up for a while but then shutting off before reaching the desired temp, then turning on again after a minute, then shutting off, and so on.

I see on other threads that short cycling is usually due to a bad flow valve. But it just seems unlikely (to me) that both the pressure switch and flow valve would go bad simultaneously.

Does anyone with expertise on this have any thoughts? Can pressure issues or a pressure switch somehow cause short cycling?

In any case, I'll remove the flow valve and take a look at it tomorrow. What's the best way to get to it on a Minimax 400?
 
Short cycling is usually the flow valve or a bad temp limit switch. You can temporarily bypass the limit switch and see if that corrects the issue. Don't leave it bypassed though. I would take the flow valve out and test it as well. Keep in mind that if those bolts are stuck, don't break them off. If stuck, use WD40 or similar and spray them and let sit for a few minutes. If you break one off, you're in for a tough time.
 

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Could also be low flow. If your outlet into the spa is not mixing in the tub with the whole volume, you may be letting the hot return water flow into the intake. Speed up the flow and then the return mixes with the spa water and then cooler water is getting to the heater.
 
From the Pentair MiniMax NT service manual

If the heater fires, shuts down and refires every 30-45 seconds and the Service Light comes ON and
goes OFF alternately with the Heat Light, this indicates that the Inlet or Outlet High Limit Switch is
sensing a temperature greater than 115° of 150° F., respectively. This is generally caused by a lack of
water inside the heat exchanger, while the heater is firing.
Things To Look For:
1. The pump is worn out.
2. The pump isn’t pumping enough water.
3. The pump impeller is plugged.
4. A valve on the outlet side of the heater has been closed.
5. The pump is a 2 speed that is operating on low speed.
6. Something is blocking the water flow through the heat
exchanger.
7. The flow valve is defective or damaged.
 
Thanks for all the helpful tips, everyone. I replaced the flow valve and the heater worked great to bring the spa up from 57 to 98 yesterday.

The old flow valve wasn't corroded at all, but the thinner spring was clearly elongated. See photo. Any ideas on what causes this?

Image: Imgur: The most awesome images on the Internet

We did have 600 sq ft of solar pool heating put in over the summer. Whenever it comes on, all the air in the heating panels gets blown through the whole system and out into the pool, as the pool water replaces all the air. There's no bypass on the heater, so I imagine the air is getting blown through the heater. Could this warp the flow valve? Or is it standard to have the pool solar set up like this?
 
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