Mastertemp 400 Short Cycles - No Errors - Prefers lower flow at start

[c379776]

If I start up my heater with a flow rate of ~60gpm (as displayed on the intelliflow) it will short cycle about every minute. If I reduce the flow to 40 the heater will stay on and after it is on for a few minutes I can dial up the flow back to 60gpm and it will continue to run and heat the pool. When it is short cycling I get no E codes or LEDs on the Igniter board or the back of the control board. The burner lights quickly and there is no rattling or odd noises. Filter is clean and am getting good flow. Pump @ 2500 = flow rate of ~60 back pressure is 22. I replaced the thermal regulator with a new one that I tested before install. The old regulator tested bad and the bypass valve is in place as best I can tell from feeling in the regulator port.

My pool has been in service for 2 years. It is indoor and is an above ground 15' x 75' x 48" plumbed with 2" PVC. 3 HP Intelliflow with intelliComm, 60sq ft DE, Gold line Salt and control, Propane Mastertemp 400.

 

[ajw22]

I would open up the header and replace the bypass valve. Replace the header O rings while you have it open. There are YouTube videos on how to do it. It is an hour or two job.

 

[c379776]

I would open up the header and replace the bypass valve. Replace the header O rings while you have it open. There are YouTube videos on how to do it. It is an hour or two job.

Thanks for the quick reply, I just can't wrap my head around how that could be the problem, plus I could feel the valve was in place and not wobbly when I replaced the regulator. The water temp leaving the heater never gets above 95 (80 in and 95 out). The stack temp is 280 and steady. I can run high flow rate after the initial two minutes, its only at startup that the heater won't tolerate flow above 40gpm. I would think that a broken bypass would cause high temps all around, if anything my temps are low. Also the heater is just out of the 2yr warranty.

 

[ajw22]

The bypass valve is letting too much pool water bypass the heat exchanger. The mix of heated water and cold pool water is what gives you low output temperature.

While the bypass valve feels good something may be wonky with the spring. Or you have something rattling around in the manifold which you will find when you open it up.

Thats my theory.

 

[c379776]

The bypass valve is letting too much pool water bypass the heat exchanger. The mix of heated water and cold pool water is what gives you low output temperature.

While the bypass valve feels good something may be wonky with the spring. Or you have something rattling around in the manifold which you will find when you open it up.

Thats my theory.

Yeah that makes sense and I'll probably have to look there next. But then why does the heater short cycle? Stack temp is good and matches my thermal gun measurement of the exhaust.

 

[ajw22]

If you really want to know flip the cover over so you can watch the LEDs as it shuts down in the short cycle and if you are quick you will see one of them blink on and off. The water is overheating internally and one of the safeties is shutting it down. But as soon as it shuts down it cools down, rests, and the heater cycles again.

 

[ajw22]

What is the water temperature reading on the heater display when it shuts down?

What is the heater set point at?

 

[c379776]

What is the water temperature reading on the heater display when it shuts down?

What is the heater set point at?

I watched the LEDs and even recorded. I'll take a closer look as the phone camera could miss a quick flicker. The temp on the display always matches the pool temp of 78-81 and is steady. Heater setpoint is 100 pool controller set at 81. I have the salt cell right on the outlet of the heater and it reads 90-94 (when the heater is firing) deg, never anywhere close to 120.

 

[c379776]

Definitely no LEDs flickering. Parts ordered. I'll check back in a few days.

 

[c379776]

I failed to mention that I am on LP. Sorry. I talked to the local Pentair warranty station guy and he said every call he has had on a Mastertemp on LP with no codes was an LP supply issue. My installer put a 5/8 corrugated flex connector from the supply pipe to the MT. I looked it up and it is rated for ~ 200K BTU for LP. I found this one rated at ~430K BTU LP: https://www.amazon.com/gp/product/B0046ECL0I/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&th=1

I'm going on the 3rd day now without any cycling. Finger's crossed, but it's looking solved.