STIEBEL ELTRON SOL 25 PLUS - Manual (Page 67)

WWW.STIEBEL-ELTRON-USA.COM SOL 25 PLUS | 67
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Fault Cause Remedy
The tank cools down excessively overnight. After the
pump has stopped, the flow and return operate at
different temperatures; the collector temperature is
higher at night than the outside temperature.
The check valve is not closed or not closing, thereby
causing thermosiphoning and heat loss from the tank
to the solar loop.
Single pipe thermosiphoning circulation occurs in
short pipework with low pressure drop.
• Check the position of the check valve handle, which
should be set for one-way flow.
• Inspect the check valve (gravity brake) for leaks
(jammed swarf, dirt particle in the sealing surface).
• Make sure the tank’s heat exchanger’s supply lines
are configured in a U (downwards) shape to prevent
thermosiphoning.
• If required, install a two-way valve that is switched off
simultaneously with the pump to block thermosiphoning
in the solar loop.
Install a check valve (gravity brake) in the flow or a heat
insulating loop.
Re-heating does not work. The boiler runs for a
short while, stops and restarts again. This
repeats frequently, until the tank has reached its
setpoint temperature. Air in the re-heat heat exchanger.
Heat exchanger area is too small.
Vent the re-heat heat exchanger.
Compare the details supplied by the boiler manufacturer
and those of the tank manufacturer. The problem may be
resolved by selecting a higher flow temperature at
the boiler.
The tank cools down excessively.
Insulation faulty or incorrectly fitted.
Re-heating controller setting is incorrect.
DHW circulation runs too frequently and/or at night. Check the insulation; insulate the tank connections.
Check the boiler controller setting.
Check the switching times and interval operation.
The pump does not stop.
Sensor faulty or sensor position incorrect.
Control unit not OK.
Check the sensor position, installation, and resistance
curves.
Note: The variable speed pump does not stop
immediately, but only after it reaches its lowest speed.
11. gLOSSARY OF TERMS
The following is a glossary of terms, definitions of abbreviations and
acronyms which appear in this manual:
absorber plate: a metal plate (typically made of copper) which has a
selective coating to efficiently convert sunlight into heat and transfer
this heat to liquid that circulates through copper pipes attached to
the plate.
after-heating: a method to add heat from a non-solar source, such
as a fuel-fired boiler, to raise the temperature of water in a storage
tank to the minimum required for end use.
altitude angle: angle of sun above the horizontal plane.
anode rod: a metallic rod that is installed in a water storage tank in
order to reduce corrosion of the tank and its internal components
by serving as a sacrificial electrolytic anode. An anode rod must be
replaced when it is depleted, otherwise the tank and/or its internal
components will start to corrode.
boiler drains: drain cocks installed in solar and hydronic heating
systems to allow portions or all of the system to be drained of their
working fluids (heat transfer media).
BSPP: British Standard Pipe (Parallel) Thread for tubes and fittings
where the threads do not provide pressure-tight sealing.
bypass valves: valves that are installed in solar heating and
afterheating systems to allow portions of the system to be bypassed
for maintenance and repair. Bypass valves are typically installed in
2-tank systems to allow flow to bypass the solar storage tanks.
charging (of system): the process of filling the solar loop with heat
transfer medium (fluid).
charging pump: a pump used to fill (charge or recharge) the solar
loop with heat transfer medium.
check valve: a special type of valve that permits fluid to flow in
one direction but not the other. It is typically used in solar heating
systems to prevent undesired thermosiphoning of heat transfer
medium when the collector pump is switched off.
compensator: a flexible stainless steel tube that is installed between
solar collectors and used to connect them to solar loop piping. The
compensator allows piping to expand and contract and mounting
hardware to move slightly under loads and thermal expansion
without placing undue stress on collector fittings. It is very
important to avoid repeated stress cycles upon fittings, as leaks may