Buderus 500 - 28/C Servicing Manual page 64

7 Actions
box 220 Check the Buderus 24V AC external
3-way valve – power supply cable
A
CAUTION!
To prevent damage, do not insert the measuring
electrodes of the multimeter too far into the holes of the
plug-and-socket connection.
Take the boiler out of operation, see box 43 or 44.
Remove the power supply plug of the servomotor of the
Buderus 24V AC external 3-way valve, see box 213.
Remove the connection of the power supply cable of the
Buderus 24V AC external 3-way valve at the boiler.
Set multimeter to "measure resistance".
Check the power supply cable of the Buderus
24V AC external 3-way valve for breaks. The electrical
resistance measured at each individual wire must be
Ω
approximately 0 .
Check the power supply cable of the Buderus
24V AC external 3-way valve for internal short circuits. The
level of electrical resistance, measured between two wires
chosen at random, must be infinitely high.
Insert the power supply plug of the Buderus
24V AC external 3-way valve.
Connect the power supply cable of the Buderus 24V AC
external 3-way valve at the boiler.
Put the boiler into operation, see box 54 or 55.
box 221 Check the Buderus 24V AC external
3-way valve – drive mechanism
Take the boiler out of operation, see box 43 or 44.
Remove the servomotor of the Buderus 24V AC external
3-way valve, see box 218.
box 222
Check to ensure that the drive mechanism of the Buderus
24V AC external 3-way valve is running smoothly. This is
done by gradually pushing the spring fully home by hand
and allowing the spring to return gradually to its home
position.
box 223
Refit the servomotor, following the above procedure in
reverse order.
Put the boiler into operation, see box 54 or 55.
We reserve the right to make technical modifications
64 Servicing manual Gas condensing boiler Buderus 500-24/S, 500-24/C and 500-28/C • Issued 02/2006
box 224 Replace the Buderus 24V AC external 3-way
valve – drive mechanism
Take the boiler out of operation and drain the heating
system, see box 48 to 51.
Remove the servomotor of the Buderus 24V AC external
3-way valve, see box 213 or 218.
box 225
Remove the drive mechanism of the Buderus
24V AC external 3-way valve using the wrench supplied
A
with the drive mechanism.
CAUTION!
Note that water will squirt out when the drive
mechanism is removed.
Have a bucket and a supply of dry cloths to hand.
box 226
Fit the new drive mechanism to the Buderus
24V AC external 3-way valve.
Connect the servomotor of the Buderus 24V AC external
3-way valve by following the above procedure in reverse
order.
Fill the heating system, vent it of air and place the boiler
into operation, see box 52 to 58.
box 227 Check the Buderus 24V AC external
3-way valve – installation
Use the letters marked on the 3-way valve to check
whether the Buderus 24V AC external 3-way valve is
correctly fitted:
A = flow of storage-type water heater
B = CH flow
AB= boiler flow
Buderus Ltd. • http://www.buderus-domestic.co.uk