Required annual maintenance
(To remove front cover, see page 12)
Maintenance must be done by a qualified contractor.
Venting system - inspect inside of flue pipe for any blockage
or restriction. Observe burner flames during heater
operation (front cover must be removed). Burner flames
should be steady and blue. Yellow, inconsistent (bouncing)
flames may be an indication of poor ventilation or
combustion air supply. Inspect the combustion air intake
pipe for blockage or debris. Inspect air intake and exhaust
terminations for blockage or debris.
Inspect burner observation window for cracks or spillage of
flue gases. Observe burner flames during heater operation.
Flames should be steady and blue with no signs of
yellowing. Yellow burner flames are an indication of
improper combustion. Refer to section 4.6 to verify the
exhaust system and combustion air supply meets the
Manually open the pressure relief valve to ensure proper
operation, make sure discharge drains away safely.
Inlet Water Filter
Verify the inlet water filter screen is clean and undamaged.
The inlet water filter is located on the top of the appliance,
at the cold water inlet connection. (See Fig. 29, page 37).
Close the installer supplied water shutoff valve purge the
water using discharge drains and remove the brass hex cap
holding filter. Remove the filter, clean and/ or replace if
In areas where the water supply has a high mineral content
(see table 17 Water Quality) the heat exchanger should be
flushed with a descaling solution. Scale build up will
shorten the life of the water heater and damage resulting
from scale is not covered under warranty. Refer to section
7.3 for detailed instructions on descaling the heat
Check for debris and clean if needed.
Greentherm T9900 SE/i – 6 720 813 635 (2019/03)
Winterizing for seasonal use
The water heater must not be installed in a location where it
may be exposed to freezing temperatures unless connected to
electrical power. All water must be drained from the heater in
order to avoid damage to the unit from exposure to freezing
Use of agents such as anti-freeze is not permitted and voids the
warranty, as they may cause damage to the water heater's
1. Hold ON/OFF switch on the water heater for 3 secs. to turn
OFF the heater and unplug the power supply cord. The
display should be blank.
2. Shut off the gas supply to the water heater.
3. Shut off the water supply to the water heater using installer
supplied shutoff valve.
4. Open hot water taps to drain and relieve pressure from the
plumbing system. If water continues to flow after 5
minutes, a crossover of the hot and cold water pipes is
present and must be corrected before proceeding.
5. Disconnect the inlet and outlet water pipes from the water
heater. Place a small bucket underneath the water heater to
catch residual water remaining inside the water heater.
6. Using an air compressor, blow short bursts of air (50psi
max) through the inlet water connection or inlet water filter
until there is no water present coming through the outlet
water connection of the heater.
7. Empty condensate trap.
8. Reconnect the water fittings and return the heater to
service when danger of freezing has passed.
Mineral scale build-up
Periodic descaling may be necessary in areas with high mineral
content in the water (See table 17 Water Quality). Scale
buildup in the heat exchanger may result in lower flow rates,
error codes of AA, E3, A5 and boiling sounds in the heat
A water softener is required if the water hardness exceeds 14
grains/gal (200 mg/l) calcium carbonate. Damage to the water
heater resulting from hard water/scale deposits will not be
covered under warranty.
Descaling using a pump
▶ Disconnect the electrical supply from the water heater.
▶ Shut off the water supply to the water heater.
▶ Open hot water taps to drain and relieve pressure from the
▶ Shut off hot water valve to the water heater.
Maintenance and service