Vaillant auroTHERM VFK 900, Start-Up, Maintenance And Troubleshooting Manual

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Manual - Solar hot water systems 0020009607_02 64
Malfunction Cause Remedy
Reheating is not working. The boiler runs
for a short time, goes off and then back
on again. This is repeated until the
cylinder is at its target temperature. 1. Air in the reheating heat exchanger Bleed the reheating heat exchanger.
2. Heat exchanger surface area too
small Compare the specifications of the boiler
manufacturer with those of the cylinder
manufacturer. The problem may be able to be solved
by a higher setting of the flow temperature at the
boiler.
Only cold or lukewarm water comes out
of the taps. 1. Cold and hot water connections on
the cylinder have been mixed up.
Turn off the cold water supply, then let water flow out
via the hot water connection. Only a few litres of
water flow out if the connection is laid correctly. The
inlet of the hot water draw-off pipe then rests in the
air space; no further emptying is possible. If the
entire solar cylinder runs empty via the hot water
connection, the connections have been laid
incorrectly. Change the connections!
2. Hot water thermostat mixer set too
low.
Increase the setting.
3. Solar heating insufficient; boiler
does not reheat.
External control device faulty.
Air in the reheating heat exchanger
Cylinder temperature sensor
defective.
Check whether the boiler is working.
Check whether the external control device is working.
Check whether the two port valve is in the hot water
position.
Replace the two port valve.
Bleed the reheating heat exchanger.
Check the thermal cut out and reset it.
Replace the cylinder thermostat.
Water flows out of the expansion relief
valve (only when heating up). Dirt on the valve seat of the expansion
relief valve. Check the expansion relief valve and reset it
manually.
Pressure limiting valve defective. Switch off the boiler and immersion heater and check
whether the pressure behind the pressure limiting
valve is lower than 3.0 bar if water flows out only
when heating up. If so, replace the pressure limiting
valve.
Expansion vessel defective. Check the pressure in the expansion vessel. If the
pressure is insufficient, re-establish the pressure and
check whether the equalisation tank maintains the
pressure.
Expansion relief valve defective. If the pressure is normal, replace the expansion relief
valve.
Water comes out of the temperature and
pressure relief valve (only when heating
up). Dirt on the valve seat of the
temperature and pressure relief valve. Check the seat of the temperature and pressure relief
valve and reset it manually.
Temperature control of the boiler
defective. Check the temperature control of the boiler if water
only comes out when reheating with the boiler.
Check whether the two port valve switches to the
heating position after reaching the cylinder
temperature.
Cylinder temperature sensor defective. Check the cylinder temperature sensor and the
corresponding thermal cut outs and replace the
temperature sensor and reset the thermal cut outs if
necessary.
Two port valve defective. Check whether the two port valve is working and
replace it if necessary.
Temperature and pressure relief valve
defective. Replace the temperature and pressure relief valve if
water only comes out when heating up with the
immersion heater.
Immersion heater defective. Check the temperature sensor of the immersion
heater and the corresponding thermal cut out and
replace the immersion heater if necessary.
Table 8.1 Troubleshooting (continuation)
8 Troubleshooting