Maybe Mastertemp 400 flow probem?

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generessler

generessler

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Dec 13, 2020
935
Chapel Hill, North Carolina
Pool Size
19600
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Jandy Aquapure 1400
Can a Mastertemp expert please help me out?

My 7-year-old heater has been cranky for a while: randomly shutting down the gas with AGS and HLS errors, but then working okay again when restarted. We don't heat the pool. Just the spa when we want to use it. Maybe 20 times a year for a few hours. So the heater sits idle most of the time. I know that's not great for the heater, but there you go.

Over time it got worse. So I replaced AGS and HLS sensors and finally the thermal regulator. OEM parts. The old regulator was definitely stuck, so thought that was it.

But no joy. Tried again today and both AGS and HLS triggered after a running maybe 5 minute.

So looking at lots of TFP threads, it feels like this is a flow problem. My flow gauge says 50 gpm running the Intellifo at 2500 RPM and the bypass is in "no bypass" position. The book says minimum is 40, and the flow sensor has never triggered. For years this seemed fine.

With the heater bypassed, flow is much higher: about 82 gpm. There are some threads saying Mastertemps have a pretty high "head loss" so never thought this was a problem.

Since the family was wanting the spa heated today I tried turning the pump up to 3100 rpm and restarting. Yay. It got to 99F successfully. The flow is about 60 gpm. With the header bypassed, it's about 100.

So I am thinking something is wonky inside the manifold and I need to take it apart. Maybe the pressure bypass is broken? But I don't want to disassemble for no reason.

Any help? Thanks as always.
 
Okay. Here we go. I think this one shows the disk. I have some different angles if not. That's the bypass valve?

While I had the regulator out, I tested it with hot water. According to our meat thermometer, it cracked open around 120F and was 3/16" or so open by 130F.

PXL_20250525_161914062 (1).jpg
 
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Okay. Just tried. It gave an HLS error after a couple of minutes at 2000 RPM. At that point the stack temp was 333.

BTW it's just awesome that you're helping especially on a holiday weekend. Thanks.

Here are some pictures. The equipment is surrounded by a gardenia hedge, so hard to get a single good pic. Smells nice tho :cool: . (Rewiring the mess is a future project.) Here the bypass is in a "mostly bypass" position where it sits when the heater is not in use.

PXL_20250525_180759584.jpg

PXL_20250525_180722106.jpg
PXL_20250525_180731585.jpg
Here's the "no bypass" position:
PXL_20250525_181044330.jpg
 
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Try trimming back the gardenia hedge. As it grows it blocks airflow into the heater, and the exhaust rising away from the heater.

The hedge creates an environment as if the heater is in a corner which often requires a chimney vent pipe to clear all walls..
 

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JamesW said:
How much is the flapper on this check valve opening?
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Completely as far as I can see. I guess I could remove the flapper and try that. But the flow gauge is saying flow is way above min.

Another bit of info is that when I'm running the normal low speed with bypass off, heater off: 1100 rpm @ 38 gpm, then switch the bypass to heater, the flow drops to just about zero.
 
generessler said:
Another bit of info is that when I'm running the normal low speed with bypass off, heater off: 1100 rpm @ 38 gpm, then switch the bypass to heater, the flow drops to just about zero.
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1100 RPM is too low to get much flow through a MasterTemp heater. The MasterTemp heat exchanger is very restrictive.

I need 2400 RPM for good flow through my MasterTemp.
 
ajw22 said:
1100 RPM is too low to get much flow through a MasterTemp heater. The MasterTemp heat exchanger is very restrictive.

I need 2400 RPM for good flow through my MasterTemp.
Click to expand...
That's what I figured. I never try running the heater that low. But the fall-off from 38 to zero on the flow meter seemed a bit weird.

I will trim the spring growth off bushes, but the photo makes it look like they're closer than they are. There's a good 16 inches all around.

Do you think it's worth taking the manifold apart just to have a look? Since it's failing with 50 gpm passing through, the only thing I can think of is something wrong with the internal bypass or otherwise messed up in there. Otoh I keep thinking "if you don't take it apart, you can't break it."
 
generessler said:
Do you think it's worth taking the manifold apart just to have a look? Since it's failing with 50 gpm passing through, the only thing I can think of is something wrong with the internal bypass or otherwise messed up in there. Otoh I keep thinking "if you don't take it apart, you can't break it."
Click to expand...
Yes.

At 5 years old I took off my manifold and replaced the thermal regulator and bypass valve. Also replaced all the manifold O rings.

This year at the 10 years old mark I replaced the manifold that included all new sensors.

Removing the manifold gave me an opportunity to assess the condition of the heat exchanger and confirm it was worth dumping money into the heater.

My 10 year old heater now runs better than the last few years and I think heats quicker.

I described what I did in…

Pool Opening Spring 2025 - Removing the Leaking Heater Manifold

Opened my pool today. Some observations: Pool opened up pretty clean. Water temperature was 49F. Leaves all vacuumed up. See pics below. I added borates the end of last year and did not see any winter scaling. pH tested way high and added 40 oz of MA to begin working it down. I had 4 gallons...
www.troublefreepool.com www.troublefreepool.com
 
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