Fault finding and diagnosis
Greenstar 4000 – 6 720 891 162 (2020/09)
80
Fig. 100 System gassing flow chart
Is your system pressure constantly increasing even
when the boiler is off for extended periods of time?
NO
NO
YES
YES
YES
NO
Is your system pressure
regularly dropping
(i.e. you constantly
have to top up your boilers
pressure)
Have you confirmed that the
filling link is not stuck
open/passing water in any way?
Does system pressure
increase when the
boiler is on?
Does system pressure increase
above 2.5bar or enter the high
pressure red zone (Max
operating pressure)
on the pressure gauge/display?
Does the
problem
persist?
NO
Does your PRV
regularly drip?
The
boiler
is
fine
Check
the CH
system for
leaks
Check/
replace
PRV
YES
NO
YES
NO
YES
The
boiler
is
fine
Check
Expansion
Vessel is sized
correctly for
the system
Re-
pressurise
the EV
Is the Expansion
Vessel pre-charged
higher than expected?
NO
YES
Is the Expansion
Vessel pre-charge
too low?
NO
YES
YES
NO
The
boiler
is
fine
Confirm the filling link is
closed and check that the
Plate Heat Exchanger
is not cross leaking
Plate heat
exchanger
leaking?
NO
Do the radiators
have to be
regularly vented?
YES
Corrosion
is probably
occurring within the
heating system which
is causing system
gassing.
The system should
be cleaned
and treated to
comply with
BS 7593
NO
Most
likely a
cross-leaking
component in
the boiler.
Further
investigation
required
YES
0010036323-001
Replace
Plate Heat
Exchanger
PRV = Pressure Relief Valve
EV = Expansion Vessel