Pentair pool heater

Hi,
I have a new pump/heater installation. All are Pentair products - filter, a new 1/2hp pump and a Minimax 100 natural gas heater, supplied as a kit from a good pool dealer. Everything is working fine - very strong flow from the pool, through pump, filter and heater, then back to the pool. Heater ignites and stays lit, burns strongly. However, the water isn't getting heated.
I noticed the 2" header on the heater includes a bypass valve. This is a small plastic disc held in place between the two halves of the header by a spring. The spring seems to me to be surprisingly weak, especially considering how well the pump works. This was the first thing that came to mind, so as a test I added a small spacer to the valve spring, effectively increasing its compression slightly. It made no difference.
So, my questions are; how long should I expect the heater to be running before I can tell there is heated water? I've waited a few minutes. Does it take a long time for the heat to penetrate the water headers in the heater? I would think a few minutes would be more than enough. Has anyone experienced a pump that is just pumping too powerfully for the heater to be effective with the volume of water? Is it common for the bypass valve to let a lot of water bypass the heater (I still think this is the most likely cause). Is it possible the heater headers are blocked (tho it's a new heater)?
Any help would be much appreciated... I'm running out of ideas! Thanks.
Pete
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Pete writes:

I hope you don't have some naive idea about pool heating.
Your small unit only delivers 80,000 BTU/hour. Let's say you're piping 50 gallons a minute. That's 50*60 = 3000 gallons per hour. 3000 gallons weighs about 25,000 lbs. One BTU is one degree F per pound of water, so the the temperature differential of your heated water will only be 80,000/25,000 = 3.2 degrees F above the pool inlet, hardly perceptible. It's not going to feel like your household hot water is running into your pool.
You will bankrupt yourself buying gas to heat your pool. Did your "good pool dealer" tell you that?
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Thanks for the info. I know it'll take a long time to heat that volume of water; when I said "before I can tell there is heated water", I just meant by feeling the outlet pipe at the heater, not the pool water. I should have been more clear. I still think I should be able to discern *some* difference between the inlet and outlet pipes after the heater has been running for a while. Another thought occured to me overnight, one that also might explain the design of the bypass valve. I think the heater currently has an airlock. If the water pressure were equal on both sides of the header, as it should be, the valve would not operate. But if there is an airlock in the main heated part, the water will pass through the bypass valve. So I suspect there is probably an air release valve or plug in the other side, in the return header. I'll check... I hope so!
Thanks again.
Pete

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Pete writes:

That would be odd. Pool circulation lines often get air going through. The heater should not be capable of air locking.
Surely this thing could not burn gas constantly (as you report) without water also going through it and not overheat. It must have an overtemperature shutoff.
I think you're just way overestimating what 80K BTUs feels like in that much flow. Or maybe just hesitant to accept that this unit isn't big enough to heat your pool, and if you had one big enough, you couldn't afford to fuel it.
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Well, I stripped it down, checked everything over, even tipped the heat exchanger on it's end, then reassembled. It worked! I guess I'll never know what the problem really was, but it works just fine now. It raises the temp of the pool by about 3degF every hour. At 77F I took a dip - bliss!
Wife returns from a trip tomorrow. She'll be pleased.... I hope!
Pete
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Pete writes:

Really? 3 deg F into 80K BTU/hr means 3200 gallons. Is your pool that small?
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