pressure may indicate a system leak; air venting
or that the system was not sufficiently charged
on installation. It is not always possible to expel
all the air from the system at the time of initial
charge, small bubbles entrained in the fluid will
take a few days to a week to collect so that the air
can be vented. If system pressure drops below
normal operating pressure after air has been
vented, the installer must top up the HTF and re-
pressurize the system.
12.2 Temperature Differential
The temperature difference between the collector
outlet sensor (T1) and the solar tank sensor (T2)
is a good indicator that the system is operating
correctly. During the middle of the day, when the
pump is running the normal operating differential
will be 4ºF – 40ºF.
If the solar tank reaches its maximum tempera-
ture the pump will stop. If this happens during
the middle of the day the collector temperature
will rise rapidly while the tank temperature will
remain static. In this case a temperature differen-
tial of up to 300°F is not unusual.
12.3 HTF Acidity
The propylene glycol HTF should be slightly
alkaline at all times, the pH can be checked peri-
odically by bleeding a few drops from the collec-
tor loop and testing with pH strip paper or other
pH tester.
Normal operating pH: 8 - 10
Acidic HTF will attack metals in the collector
loop and result in decreased system life and poor
operation. If the pH of the HTF falls outside the
normal range, contact your installer, drain the
system and replace the HTF.
Propylene Glycol Maintenance Schedule
Date Of Installation:
Date Of Service:
Date Of Service:
Date Of Service:
Date Of Service:
P.31
