Pentair Mastertemp 250 fires and runs, but shutting down intermittently before temp reached (Service Heater led, no other indicators)

[Websherpa]

I'm looking to see if my symptoms fit with a typical scenario before I call in the pool guy (who around here will try to sell me a new heater).
Pentair Mastertemp 250 (Canada), installed 2015, the older un-connected control board and 5 button panel. SWG DE inground Pool.
Has worked pretty flawlessly since install (while I've watched neighbours' Haywards go up in smoke, literally). Towards end of last season I noticed it reported seemingly lower temps than the pool thermometer and had to be "upped
" a few degrees to get to the temp we wanted. (I have replaced the keypad in year or two prior.)

This season while starting up I noticed some mice turds and mouse grease in the white air orifice. Nothing chewed. Cleaned the orifice, took it off, blew out the blower, it spins freely.

Heater starts up (R13) and ignites, exhausts as as normal.
256 - 303f stack temp water speed dependant
I do hear some air gurgle through each time it re-starts, but I don't see any apparent leaks.
I've noticed that I like a hotter pool the older I get. (slipped that in to see if anyone is still reading. )

Shuts down before target temp reached, "Service Heater" light, no other diagnosis LEDs lit. Controls lock out, usually I turn off and on again, but I believe that it will try to cycle and sometimes comes back on for a bit.
Amount of time before shut down varies quite a bit, from a few minutes to hours.
I noticed once or twice that the reported water temp was a few degrees higher than it really was, but it also shows normal most of the time (and I set target temp much higher to try to keep it going). Always get the Service Heater led when it shuts down.

Are there any typical cuplrits to look for or easy parts replacements? (I am handy and know how to use a MM).
My chemistry is kept pretty darn near perfect and normally CSI tends more towards negative. It is also a borated pool.

So I am wondering if first step would be to inspect and replace the Thermal Regulator or ?

(Thank you in advance for any help!!)

 

[ajw22]

Check the thermal regulator. Remove it and see if it opens at 120F in hot water.

Remove the thermal regulator and as a test only see if the heater runs normally without it.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

 

[Websherpa]

Check the thermal regulator. Remove it and see if it opens at 120F in hot water.

Remove the thermal regulator and as a test only see if the heater runs normally without it.

Pentair MasterTemp Heaters - Further Reading

www.troublefreepool.com

I finally got a chance to pull the thermal regulator. It doesn't close completely.
I got a cheap replacement, as that was the quickest, and it doesn't open until 180F .... should I spend 5 x the cost to get an OEM one?

 

[Poolbreh]

I do hear some air gurgle through each time it re-starts

Where? The exhaust? To you inspect combustion chamber for water when you removed the blower?

 

[Websherpa]

Where? The exhaust? To you inspect combustion chamber for water when you removed the blower?

No, air gurgling through pipes on start, likely not a problem. Although I need to replace that thermal regulator, I think the thermister is giving wrong temp too.

 

[ajw22]

I finally got a chance to pull the thermal regulator. It doesn't close completely.
I got a cheap replacement, as that was the quickest, and it doesn't open until 180F .... should I spend 5 x the cost to get an OEM one?

I just buy genuine Pentair parts. The problems generic parts cause are not worth the savings to me.

 

[mcinlb]

Definitely go with an OEM Pentair thermal regulator before you change anything else. I went through 3 aftermarket thermal regulators and none of them opened properly at 120 degrees which would trigger the HLS and cycling above 85 degrees.

 

[Websherpa]

I have the OEM parts finally: Thermistor (temps way off, unless it's my Control Board) and Thermal Regulator (stuck open).

Before I install them, a quick visual check did not show Manifold Bypass Valve stuck open. Is there any reason the manifold should be opened and cleaned and/or this part be replaced simply as "preventative" maintenance?

 

[1poolman1]

I have the OEM parts finally: Thermistor (temps way off, unless it's my Control Board) and Thermal Regulator (stuck open).

Before I install them, a quick visual check did not show Manifold Bypass Valve stuck open. Is there any reason the manifold should be opened and cleaned and/or this part be replaced simply as "preventative" maintenance?

I always replace both as whatever damaged the thermal regulator (chemistry) will also affect the spring on the bypass valve. Only had to come back and do the job once (for free as I told the customer the heater was "fixed") because the other part failed to always do both. More difficult, yes.

 

[Websherpa]

Well I replaced the Thermistor (no corrosion), Thermal Regulator Kit (it was stuck slightly open), and Manifold ByPass Valve (no corrosion), and the heater doesn't shut down prematurely with a Service Heater light. However the temperature shown is consistently about 7 degrees higher than it actually is.

Would this automatically be the control board? Any adjustments to calibrate it?

While in the manifold I could see that I need a new set of seals, there is some corrosion on the lower bolts, the 3/4" Pipe Plug and some of the other sensors.... although they "appear" to be functioning still.

Next steps?

 

[Websherpa]

I managed to make my last post to the wrong thread!

Conclusion: I replaced the control board (and membrane keypad) with the newer version (mine is the older unconnected heater), and it’s operating fine and showing correct temp again.

It briefly shows an AFS error when starting the heater but that doesn’t appears to be causing it not to work. I’ll check that part next.