Heater Pressure Switch Question

sjsoldo

Well-known member
Jul 17, 2009
76
#1
Need some help. Have a Pentair Minimax NT 250 heater. I know what you are thinking, and you correct. This is a crummy product and indeed it is. But cheaper than a brand new unit.

I have a Pentair VF pump, and run it for about 12 hours a day.

Here is the problem. With "energy efficient" settings, it does not trigger the pressure switch and the heater will not turn on. However, the pump will trigger the pressure switch when 1) The pump turns on, as there is high volume/pressure of output during the priming cycle and 2) When the pump switches to a programmed cycle for the pool vacuum, similarly high volume/ pressure.

Note that when the filter starts to build up pressure (i.e. the filter needs to be backwashed), the pressure switch is triggered and the heater turns on consistently.

Do any of you have suggestions? I live in Socal where electricity is expensive, so I would rather not have to turn up the output of the pump.
 

JamesW

TFP Expert
Mar 2, 2011
13,049
#2
Since the heater should be after the filter, a dirty filter should reduce flow to the heater.

Only if the heater was between the pump and filter would a dirty filter increase the pressure on the heater pressure switch.

Instead of a pressure switch, you could install a flow switch set to the correct minimum flow for your heater.
 

GoGrabTheNet

Well-known member
Dec 13, 2015
65
Phoenix, AZ
#3
sjsoldo: My apologies for my last bit of advice, in case you read it. Don't be messing with any wires!

Upon review of the manual for your heater, the Pentair Minimax NT 250, it refers to the water pressure switch being activated/ON at a (back)pressure of 1.5 PSI. This is quite low, but as JamesW mentioned, the heater should be after the pump, so the pressure-gauge reading on your filter will not be the same as in your heater. Furthermore, to go lower than 1.5PSI may be indicative of too low of flow as well, therefore causing overheating of the heat exchanger.

Since you have a VF/VS pump, try to find the sweet spot of the lowest RPM that turns on the pressure switch. I would surely hope that it's less than full-speed or "vacuum" mode.
 

CountryBumkin

Bronze Supporter
Jan 9, 2017
124
Orlando/FL
#4
That's similar to the problem I had with my SWG. When the pump was on "Low speed" there was not enough water flow to let the SWG run. So in order to get chlorine in pool the pump had to run faster.
I think you will find the same thing on your heater. You will need to increase the pump's flow/pressure some to get it working. Just decrease the run time by an hour or two if you want to keep electric cost the same.
Good luck
 
Last edited:

ps0303

TFP Expert
In The Industry
Jul 6, 2011
3,959
FL
#5
You have to bump up the speed of the pump so that the pressure requirements are met for the heater. Do NOT change the pressure switch at all if you get that advice. It is set for a specific pressure and the only time you would need to adjust it is if the heater was located in such a way that the downward pressure of the water from the pool would cause the heater to fire when the pump is not on. That is the function of the pressure switch.

Also as mentioned earlier, when the filter is dirty, the heater should be installed after the filter, it would prevent the correct pressure of water flow thus preventing the heater from firing.
 

Pool Clown

In The Industry
Sep 5, 2008
1,836
Silicon Valley, CA
#6
If you have a VARIABLE FLOW (VF) pump, and you are running it in true flow mode (turnover/time), the only way to get more system pressure to fire the heater (increasing system pressure downstream of the filter) is to either decrease the run time (this will increase the flow rate or speed to satisfy the turnover requirement in the time given), or increase the turnover (this too will increase flow to satisfy turnover rate). Oddly, cleaning the filter will actually slow the pump down. Less restriction = more available flow, and pump will compensate to maintain turnover rate (slow down).

You could run the pump in manual mode, but that will disable all the pumps safety features.

This is a great pump for commercial application where the city/county requires a given turnover per 24 hrs. You can just set it and forget it. However, it is a headache for residential application just for this reason. That's why i don't sell this pump in a residential application.

On the other-hand, If you have a VS pump, you can just start increasing the rpm till you find a speed that will fire the heater. Usually, you can get it to fire the heater and still get plenty of energy savings.

And like Paul suggests, please don't mess with the heaters' pressure switch!
 
OP
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sjsoldo

Well-known member
Jul 17, 2009
76
#7
Okay, I opened the unit and found the pressure switch. The current switch is NOT adjustable. The Pentair part # is 472125 which is not made any more, the replacement on several websites is Part #473605 which is adjustable. I will call Pentair tomorrow to confirm this.

I understand all of you are pool professionals and will know more than I ever will. All of the above recommendations (which I appreciate) say to adjust the pump output adequately to trip the switch. But what if I replaced the old switch with the new adjustable switch and tweaked it so the switch would trip at a reasonable pressure?

One thing I have not mentioned, is that this worked fine for years !!! This summer with the same settings, the switch will not activate. The only difference is that I had to replace the drive unit on the VF pump because it failed.

Once again, appreciate your input.
 

Pool Clown

In The Industry
Sep 5, 2008
1,836
Silicon Valley, CA
#8
One thing I have not mentioned, is that this worked fine for years !!!
That is exactly why you shouldn't need to adjust the pressure switch!


The only difference is that I had to replace the drive unit on the VF pump because it failed.
You could replace the switch, but i would NOT adjust it! You need to "tweak" the drive speed. You may not need to raise it much. Even a few hundred RPM isn't going to make alot of difference in your bill.
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
3,959
FL
#10
The pressure switches are set at the factory and do not need to be adjusted unless your pool sits higher than the heater and the downward water pressure would cause the heater to fire or continue running when the pump is off.

So adjust the pump speed to properly get the heater to fire.
 
Apr 12, 2018
6
akron, ohio
#11
our pool sits higher than our heater, and just recently noticed that the heater will spark and run when the pump is off, due to the "downward water pressure"...

the heater came with the house, and this is the 4th year with the pool... i never noticed this in prior years, and who knows if this was adjusted when the heater was installed...

where is the pressure switch and could i make minor adjustments so the heater will not run when the pump is off?

it's a raypak p-r266a-en-c (with a Trane label on the front)...

thanks

The pressure switches are set at the factory and do not need to be adjusted unless your pool sits higher than the heater and the downward water pressure would cause the heater to fire or continue running when the pump is off.

So adjust the pump speed to properly get the heater to fire.
 

Pool Clown

In The Industry
Sep 5, 2008
1,836
Silicon Valley, CA
#12
our pool sits higher than our heater
When the heater was first installed, the tech should have adjusted the pressure switch for this condition. If you need to replace that pressure switch, it too should be adjusted... probably by a tech so it won't "run on" with the pump off. Or by you if you are comfortable doing it. Otherwise, hire a tech...
 
Apr 12, 2018
6
akron, ohio
#14
How much higher is the pool?

i would guess the pool bottom drain is maybe 2' above the level of the heater, and the skimmer about 8-10' above the heater.

the heater sits in a "sub basement" along with the other pool equipment, below an office and sunroom that i believe were added to the house with the pool at least 30 years ago.

do you think the pressure switch is bad and not just out of adjustment?

the heater seems to run fine, except the pool head pressure makes the heater think the pump is on all the time.

thanks for the quick reply.

any opinion on the "fireman switch" with an intermatic timer?

i am going to replace an existing digital sprinkler timer with an intermatic that i had on my last pool. the last pool had no "fireman switch" with the intermatic, and wonder why i'd need one now?

thanks again,

kc
 

JamesW

TFP Expert
Mar 2, 2011
13,049
#15
The regular pressure switch can't be adjusted that much. You need a different pressure switch or a flow switch (assumes that you have the regular pressure switch).

There is a 1.75 psi pressure switch and an 11 psi pressure switch. The 11 psi switch should have been installed or a flow switch should have been installed.

The fireman's switch is a good idea.
 
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OP
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sjsoldo

Well-known member
Jul 17, 2009
76
#16
How much higher is the pool?
It is an inground pool. The heater is about 3 feel above the pool level and the pump about 2 1/2 feet.

FYI this post was from last summer. I replaced the pressure switch and the system works fine !!!!
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
3,959
FL
#18
our pool sits higher than our heater, and just recently noticed that the heater will spark and run when the pump is off, due to the "downward water pressure"...

the heater came with the house, and this is the 4th year with the pool... i never noticed this in prior years, and who knows if this was adjusted when the heater was installed...

where is the pressure switch and could i make minor adjustments so the heater will not run when the pump is off?

it's a raypak p-r266a-en-c (with a Trane label on the front)...

thanks
Yes that is the only time you should adjust the pressure switch when the pool sits up higher than the heater and the waters downward pressure can cause the heater to light when the pump is not running. I usually connect the heaters power into the pump timer and so the pump has to be on in order for the heater to get power. Then also a best practice to use the heaters on/off switch to control it as well. The OP has a different issue than you. It's always best to start a new thread so that your issue won't get confused with someone else problem. it as well.