Heater fires but shuts off

[Chief2505]

So I opened the pool and everything is going great. I replaced the sand filter with a Doheny 425 cartridge filter. My pressure started at 18 psi on the cartridge filter.
Yesterday I decided to fire up the Rheem/Raypack gas fired heater. It sensed the water temp, sensed I had flow, sparked and the fire lit and started heating the water. Initial water temp was 70, with in about 15 minutes the heater shut off. The control panel said no demand, water temp 93 which is what I had it set at. I turned the heat up to 104 and the heater fired and started heating water. But in about 5 minutes it shut off and said no demand water temp 104.
Obivously the water is no where near that temp. Reading the manual the system appears to be working as it is supposed to accept that the actual water temp is no where near what the control panel says it is.
The pool place tells me I need to call Rheem for warranty. I said I do not care about warranty I just want a functioning heater. The pool place called me back and said well we sold you that heater, we installed it for you but we cannot service it for you. You need to call Rheem. I called Rheem, they said we do not deal with the public direct, go to our website and find a pro in your area for pool and spa heaters. I did that, there are none.
So my pressure today is up to 20 on the cartridge filter. Could that 2 pounds be causing just enough restriction that the output temp sensor is not getting enough water to read accurately? I read on here that 90% of all heater problems are flow. Did I restrict the flow too much by installing a cartridge filter system?
Worthless Aloha pools in Jackson cannot even send someone until June 5, probably will not need the heater by then. Any suggestions?

 

[PoolGate]

It is more likely the temp sensor is bad. They do go bad it is not uncommon. Replace it and see if that solves the issue.

 

[Chief2505]

I took the side cover off and there is a plate over the top of the sensor and pressure switch that is supposed to protect those from the elements. That plate was pushing down on the sensor wires so I took it out and turned the sensor a little. I also manipulated the plate a bit so that it would not hit the top of the sensor. But when I turned the water back on the sensor was leaking!! So off to Amazon to get a new sensor!

 

[Chief2505]

Oh I was also able to get into the diagnostic screen and this heater only has 10 hours on it, 45 cycles and says sensor error as well as pressure switch. I might need to adjust the pressure switch but we will find that out after I install the new sensor!

 

[1poolman1]

Oh I was also able to get into the diagnostic screen and this heater only has 10 hours on it, 45 cycles and says sensor error as well as pressure switch. I might need to adjust the pressure switch but we will find that out after I install the new sensor!

Pressure switch virtually never needs to be adjusted unless your equipment is far below the pool. Then, it will cause the heater to want to stay on, not fail to light.
That error will pop up if the heater is turned on before the pump has fully primed, RPM too low on a VSP, if the filter is very dirty (at 2psi rise yours isn't), if the pump or skimmer basket is full. Its not an error with the switch, its just telling you the switch didn't allow the heater to fire. Really, anything that will interfere with proper water flow will cause that error to appear.

 

[Chief2505]

As a follow up to my heater problem. I did order a new sensor and this morning I was watching videos on how to install it. It was at that point that I realized my sensor rod was not inserted into the fitting hardly at all. Most of the sensor rod was exposed. I reinstalled the sensor making sure to seat it as far in as I could, reset the error code.
Fired the heater up and now 30 minutes later it is still heating and the water has come up from 72 to 74! I think I fixed it!! Thank you everyone for all the help!!