Overheating at Solar Collector, June 2011

Solar Thermal System has been running since late January and had an issue here in early June 2011. I checked the display and found that sensor #1 (on the collector was at over) 370°F!
Display showing hot Solar CollectorDisplay showing hot Solar Collector
Display showing T2 lower sensor in the solar hot water tankDisplay showing T2 lower sensor in the solar hot water tank
Display showing T3 which is top of the solar hot water tankDisplay showing T3 which is top of the solar hot water tank
After purging the thermal solar loop, add 30 psi to expansion tank to build up pressure in the loop.After purging the thermal solar loop, add 30 psi to expansion tank to build up pressure in the loop.

Solar utility purge pump: This picture is of the setup to purge the thermal solar loop with a utility sump pumpSolar utility purge pump: This picture is of the setup to purge the thermal solar loop with a utility sump pump
From Lowes manual Utilitech submersible utility pump, 1/3 HP, 1800GPH or 6814 L/H, #0094086From Lowes manual Utilitech submersible utility pump, 1/3 HP, 1800GPH or 6814 L/H, #0094086
The [!] was on, which means the controller has shut off the system pump to protect the lower parts from heat damage.
I manually forced on the pump which did cool the controller to 260F area but the flow was erratic to none, because of air in the system. The SR868C8 calls this the EM or emergency collector temperature or emergency swithchoff temperature of the collector. There are 2 EM parameters that are adjustable. EMOF (emergency collector maximum Switch Off Temperature) and EMON (Emergency collector maximum Switch On Temperature). Default EMOF is 120C or 248F. Default EMON is 130C or 266F. I describe this below.
I had been purging the closed loop system with a small automotive pump along with the solar pump to have a all liquid loop with no air, no cavitation. This took a while. So I purchased a utility pump like a sump pump. The next morning I placed the pump in a 5 gallon bucket with a couple of gallons of water.
Both inlet and outlet openings are under the water line with a valve shutoff blocking the loop and forcing the flow into and from the open top bucket. Within a minute the loop was purged and the collector temperature and the tank lower temperature were the same.

EMOF Function description: When temperature of collector rises up to the preset maximum switch-off temperature, collector emergency switch-off function is activated. As the result of this function, solar circulation pump is stopped,it avoids the damage of system components caused by
over-heated temperature. EMOF parameter is for set maximum switch-off temperature
of collector (factory set: 130°C), if the collector temperature rises up to preset EMOF
temperature, solar pump is stopped;EMON parameter is for set maximum switch-on
temperature of collector (factory set: 120°C),when the collector temperature drops to
EMON temperature, solar pump can be triggered again, collector emergency switch-off
function is deactivated automatically.


There are at least 3 different maximum temperature parameters that can be adjusted with the SR868C8.
*Maximum Emergency Collector Temperature, EM
*Maximum Collector Temperature, CMX
*There is also a Maximum Temperature for the Hot Water Tank, SMX

CMX Maximum limited collector temperature (collector cooling function)
Function description:
The collector cooling function delays the vaporization of the heat transfer fluid. Shortly
before reaching the maximum temperature of the collector, the solar pump starts
working in order to cool down the heat transfer fluid using the heat losses occurring in
pipelines and storage cylinder.
When tank temperature rises to its preset maximal temperature, solar circuit pump is
ceased compulsively even the temperature difference is satisfied. If the sunshine is
very good, as a result collector temperature will rise continuously, when collector
temperature rises up to its maximal temperature, solar pump will be triggered again
even at the case that tank temperature is already to its maximal temperature. And solar
pump works until the temperature of collector drops since this reversed circulation or
when tank temperature rises its emergency temperature (95°C).
When displays, and blinks on the screen, it indicates that tank emergency
temperature reaches, tank temperature is ≥95℃
SMX Maximum temperature of tank Description:
When the DT between collector T1 and Tank 2 caters the switch-on DT of circulation,
solar pump is triggered, but in order to avoid the high temperature inside tank,
controller will check whether the temperature (T3) of top part of tank is higher than
maximum temperature of tank, when T3 is higher than preset SMX temperature, solar
pump is ceased even at the case that DT caters condition. When tank temperature
drops and is 2oC below the SMX, solar pump restarts when DT caters condition.