MM PS360 - Went down to 200F and would'nt go up from there.

So my MM PS360 is always set at 440F and Sunday night I noticed that Pizzas and everything else were not coming out as baked as they should be all of a sudden. I checked the temp on the display and it was setup to 440F but then it read 200F. The gas would still kick on/off and stayed right around 200F. No idea why it did this so I turned the top unit off and used the bottom unit the rest of the night.

I replaced the Burner Blower on that unit back in Early October because it stopping heating all together and it’s been fine ever since.

I turned it on today and it’s back to working normal. What could be the issue? Thermocoupler?

Thanks all!

Unlikely to be the thermocouple.

Most likely to be one of the cooling fans in the back of the oven is clogged or totally stopped up.

Could be the centrifugal switch in either one of your blower motors - or could be a blower motor itself. The motors have switches in them that “connect” the power to the heating circuit. These switches “turn on” when the blower motor is spinning. If the blower motor is bad, or the switch is bad, the oven will do everything except heat.

Could also be your temperature controller.

Wait - I missed the “gas would still kick on/off” part.

Are you sure? It was kicking on/off just enough to keep it at 200?

Yes it was still acting normal, gas on/off and stayed around the 200F so up to 210F then down to 190F then kick on and back up to 210F and so on. Just as if I set it to 200F on the controller.
Hasent done it all day today so I dont know what the deal was with it.

My first thought would be a high limit sensor going south if it was holding at 200… Either that or the control cabinet got too hot…

Ps360 do not have a high limit

Only a thermal protection built into blower motors

Best get a service man in to check it out

Due to the way PS360s are protected, the fact that the gas valve was working and trying to get to temperature tells me that

1 of 3 things have happened, and they have all 3 have happened to me

  1. moisture in propane tank freezing up your regulator limiting propane flow( pour hot water on regulator, you will hear it thaw sounds like a whistle

  2. the flame sensor has a soot build up on ( this is caused by uneven fuel air mixture, the burner blower air adjuster wheel can vibrate loose and close up making the oven run really really rich causing extreme sooting of the flame sensor)

when this happens its not allowing the gas valve to say open creating an on and off situation over and over while the spark control module ( Could be a ignition modual but thats less likely) is looking for flame verification. In order for the gas valve to be opening and lighting or trying to light, every other system must be properly working on the oven, IE blowers, burner blowers, axial fan motors, temp controller etc etc

  1. This is the crazy one, still applies to the soot issue. Your pilot orifice has cracked and its not regulating the pilot flame properly allowing soot build up. This happened to me back in 2012, took me about 3 days of fucking with it back and forth, trying everything. No one, even middlbey had heard of this happening however it happened to me, i pulled apart the tube where the pilot O is and it fell out in 2 pieces it vibrated apart somehow or was made wrong. One of the hardest things to diagnose ever

I know these ovens most likely better then anyone here and thats where i would start.
Well thats the PMQ oven lesson of the day, lol

For some reason this issue has not come back since… but I went ahead and checked the air adjuster wheel, it’s still set to the same since I installed it a few months ago. Where is the Flame Sensor so that I can check it?

On another note, the BOTTOM oven that I use for maybe 1 hour 3 times a week decides to flip out on me know. WTF! I created a new thread so it’s easy for everyone to search when they have this issue:

Thanks all for the help!

After reading the other thread and finding the troubleshooting, I’m guessing your particular oven does have a high limit control separate from the temp controller. If it does this again, can you get a pic of the controller screen when it’s at 210 and shutting down?

My MM PS360 turns on but doesn’t light/heat up. Anyone had this before?

Couple times, pretty sure it was the gas valve both times.

What did you do to fix it?

Well it just started happening again this past week about once every other day. It would drop and stay around 200f and go up and down accordingly as the heat turns on and off.
The controller looks normal, no faults or anything during this time and when shutting it down completely.

The NEW Burner blower air wheel is still in its regular position nice and tight.

Where are the Pilot orifice and flame sensor located for me to check them out?

You might consider going to a rotating oven schedule. Every day we switch the oven that we are using, just taped an oven schedule on the side of it next to the controls. The oven gets even wear this way and hopefully will prevent a situation where your rarely used oven does not work when your workhorse breaks!


Called my repair guy. I do not have the time to work on the ovens.

Thermal High Limit Switch was cracked. Was hoping it was simply the thermocouple, as I had an extra in storage but a las it was not the culprit. Twas the thermal high switch, in the electrical cabinet, with a crack. $325 labor plus the part and I’m back business. Why it had to happen on a Sunday rather than a lowly Tuesday, I don’t know.

A Ps360 doesn’t have a high limit switch in the control box

each blower motor has a thermal limit switch on that back of the motor that cuts power if they get over temp, but there is no high limit switch to speak of as some ovens have

i guess in a way its the same thing

We’ve narrowed the issue down… seems to only be happening after about 20 minutes of the bottom oven being on. The bottom oven only stays on for about a total of 30 minutes to bake bread then it’s off the rest of the day. But the top ovens issue will happen and stay around 200f until about 30 minutes after the bottom oven is off (cools down). Then the top oven goes back to normal. We dont noticed the oven is not at temp until we run something through it and it comes out raw. Today I heard like a spindle or something startup, so i immediately went to the oven and hit the temp to see where it was at, and it was at 200F and raising and went to 440F and was fine ever since.

So it MUST be a heat sensor?
But where are these sensors located at for us to check?

Thanks all!

We had a stack of Middleby 570s that would occasionally have one start losing temp. It might happen on any of the three, but only happened if all three were on. A bunch of parts were replaced but the problem continued to happen. Somehow it was finally figured out that our gas pressure wasn’t consistent and that was causing the problem. 9 out of 10 gas pressure readings would show plenty of pressure but once in a while it would drop, causing one of the ovens to cut off. A new gas meter fixed the problem once and for all.