Pentair Minimax Plus 400 Water Heater running but not heating

New2water

LifeTime Supporter
Jun 28, 2011
78
Stockton, CA
I have a Pentair Minimax Plus 400 gas heater. It is about 60 degrees here. Grand kids are visiting so I turned on the heater to heat my pool/spa. It has been running for 6+ hours with plenty of hot air near the heater but not even warming the outgoing water pipe. There is a cast iron manifold where the water inlet and outlet are connected but that manifold is also cold. All lights are normal, thermostat setting are at high and switch is set to Pool. The burners are running. It this normal behavior? Is there a troubleshooting guide available for this unit? Any and all help will be appreciated.
 

jblizzle

Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
43,238
Tucson, AZ
If there is fire and there is water flowing through the filter, then it has to be heating the water ... there is no other option.

Are you sure the valves have water flowing through the heater? If the flow sensor failed in the heater, and you do not have water going through the heater, that could explain what you are seeing.

What is your water temperature? Are you sure there is no higher temp entering the pool? It may only be a couple of degrees warmer.

You have 150,000 pounds of water. I takes 1BTU to raise 1 pound by 1 degree F. Your heater should be adding ~320,000 BTUs per hour. So you should be getting about 2 degrees rise in pool temp every hour. So over 6 hours, your pool should have raised by around 12 degrees.

If the water started around 50 degree, it may only be up to 62 by now which is still going to feel very cold.
 

New2water

LifeTime Supporter
Jun 28, 2011
78
Stockton, CA
Thank you for your kind guidance.
All my pumped water flows to the heater after passing through the filters. There is no alternative path unless the valve is inside the heater. If I turn off the pump, the heater turns off which tells me the flow sensor may be working.

I have tried heating only the Spa (switch to SPA position, water circulating through the spa only) and it seems to be warming the water a bit. I am going to get a good thermometer and start measuring it.

One strange thing I noticed was a lot of white smoke for the first half hour after starting. There was no smell so I suspect is could be steam. If I put my hand over the exhaust grill after 8 hours of running, it gets moist as if there is steam. There is no visible water leakage around the heater. Should this be cause for concern?
 

jblizzle

Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
43,238
Tucson, AZ
That would make me want to inspect the heater really well. However, one byproduct of combustion is water vapor, so could be normal.
 

schoolpoolboy

LifeTime Supporter
Dec 24, 2013
52
San Diego
RE: "condensation" I don't recall ever seeing white smoke from my minimax plus 400, But I do know she will produce enough condensation, that you can actually hear intermittent hissing from drops of water hitting burner. And from everything I've learned, this condensation is not abnormal, and can be expected.

RE: "no heat pool/spa" Not sure what the problem is there?, but would like to hear if you did or didn't find a solution. Please post your findings.

PS: I googled minimax manual, and found several sites that offer a downloadable/printable version, but frankly the trouble shooting section is limited and doesn't really help much.

Pentair.com has a "contact us" section, where they will assign a tech to help you via email?, It's not a particularly efficient way to go,(I spent a couple weeks corresponding), but... i did find it effective, and it was FREE!

Good Luck
 

swimcmp

In The Industry
Nov 8, 2011
1,085
Moberly,MO
As per Pentair you should not use a heater to try to raise water above 65 degrees. By trying to bring the water temp above 65 you are creating condensation that is falling down onto the burners and lowering the efficiency of the heater and the life span of the burner.
 

danpik

TFP Guide
Jun 4, 2012
1,752
western NY
As per Pentair you should not use a heater to try to raise water above 65 degrees. By trying to bring the water temp above 65 you are creating condensation that is falling down onto the burners and lowering the efficiency of the heater and the life span of the burner.
Can you post a link to where you read this? I know what you are trying to say, but I don't think the translation came out right. I work mostly on home heating boilers and it is true that you need to watch the return water temp back to the boiler as it can cause condensation if the boiler flue temp gets too low.
Thanks
 

schoolpoolboy

LifeTime Supporter
Dec 24, 2013
52
San Diego
Pentair tech Anthony told me that the hissing I was hearing from water drops was normal and to be expected? I guess this may not be entirely true?

- - - Updated - - -

As per Pentair you should not use a heater to try to raise water above 65 degrees. By trying to bring the water temp above 65 you are creating condensation that is falling down onto the burners and lowering the efficiency of the heater and the life span of the burner.
Really? what should one use to raise water temp above 65?
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
4,049
FL
What do the flames look like coming off the burners? You might have flames but very weak and so it appears to be heating but will take forever. Is this a natural or propane gas heater?

swimcmp, what are you talking about?????
 

swimcmp

In The Industry
Nov 8, 2011
1,085
Moberly,MO
Just attended a two day Pentair tech school and the lead trainer on heaters discussed this. Pool heaters are not designed to operate under 65 degrees. The problem is when water temps are that low the heat exchangers condensate to much and you do not get efficient heat transfer. You mainly get white smoke which probably is vapor.
 

Rocco

Well-known member
Dec 23, 2012
261
Manassas Park, VA
swimcmp,

Thank you for the clarification. So if I understand correctly it is best and recommended to only use your heater if the pool water is already above 65 degrees.

I also hear the water drip into the flames every now and then. This is good news because I thought I had a small hole in my heat exhanger.
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
4,049
FL
This is do in part to their canister design. Raypak/Rheem states not to operate at temps at or below 50 degrees. Raypak/Rheem wins!
 

swimcmp

In The Industry
Nov 8, 2011
1,085
Moberly,MO
Minimax is not a canister design. Minimax is built just like Raypak/Rheem as the heat exchanger is above the burner tray allowing condensation to drip onto it.
 

schoolpoolboy

LifeTime Supporter
Dec 24, 2013
52
San Diego
Just attended a two day Pentair tech school and the lead trainer on heaters discussed this. Pool heaters are not designed to operate under 65 degrees. The problem is when water temps are that low the heat exchangers condensate to much and you do not get efficient heat transfer. You mainly get white smoke which probably is vapor.
So when you say, "not designed to operate under 65 degrees", Do you mean ambient temp? or water temp?

I live in San Diego where the temp drops below 65 about twice a year.(exaggeration), My point is, I've never been around my mini while it's running when I DIDN'T hear condensation hitting burner. No matter what outside or water temp is?, she always intermittently hisses.

Also, It's possible I missed something but, I looked in my owners manual and couldn't find anywhere that said not to operate if outside or water temp is below 65?
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
4,049
FL
Also, It's possible I missed something but, I looked in my owners manual and couldn't find anywhere that said not to operate if outside or water temp is below 65?
If you have the MiniMax Plus manual, look at page three, Introduction, and you should see this:

OPERATING THIS HEATER CONTINUOUSLY AT WATER TEMPERATURE BELOW 68° F. WILL CAUSE
HARMFUL CONDENSATION AND WILL DAMAGE THE HEATER AND WILL VOID THE WARRANTY.


The interpretation of this is, you CONTINUOUSLY, do this it can damage the unit. The key word is CONTINUOUSLY. So if you occasionally do this then they are saying it's OK.

This is just my interpretation of this caution in the manual. I don't see how a customer is going to know this or is going to remember this or is going to NOT heat their water when it gets cold. After all, a heater is to heat water.
 

schoolpoolboy

LifeTime Supporter
Dec 24, 2013
52
San Diego
If you have the MiniMax Plus manual, look at page three, Introduction, and you should see this:

OPERATING THIS HEATER CONTINUOUSLY AT WATER TEMPERATURE BELOW 68° F. WILL CAUSE
HARMFUL CONDENSATION AND WILL DAMAGE THE HEATER AND WILL VOID THE WARRANTY.


The interpretation of this is, you CONTINUOUSLY, do this it can damage the unit. The key word is CONTINUOUSLY. So if you occasionally do this then they are saying it's OK.

This is just my interpretation of this caution in the manual. I don't see how a customer is going to know this or is going to remember this or is going to NOT heat their water when it gets cold. After all, a heater is to heat water.
Thank You ps303

Your right, and not only is that "warning" nonsensical and ridiculous, It's also vague in it's wording.

What EXACTLY do they mean when they say, "continuously"? 24hrs?, a week?, a month?, a year?

Further more, If continuously operating heater at temp below 68 will damage heater? Then why not make minimum thermostat setting 69 degrees?

Because 99.9% of the time water temp is going to be below 68 when you fire heater up. So theres always going to be a period of time when heater is running when temp is below 68, causing condensation.

So instead of Pentair placing warning?, They should engineer their product in a way that will allow start up with temp below 68, but WILL NOT allow to operate "CONTINUOUSLY" unless temp is 69 degrees or higher.

Should this post be in the "Rant" section? lol