Potterton MULTIPOINT Installation And Service Instructions Manual page 17

Replacement of Parts - Page 17
6.11. HEATING UNIT
a. Gain general access - see 6.2.
b. Drain the appliance - see 6.6.
c. Remove the 2 screws securing the energy cut-off
device to the heating unit (located top front left).
d. Remove the thermostat phial from its pocket - See 6.9c.
e. Disconnect the 2 unions.
f. Remove 4 screws securing the unit to the chassis.
g. Carefully pull the unit from the top and lift. DO NOT
lose the 'O' rings and washers.
h. Remove the primary flue, secured by 4 screws (2 front,
2 rear).
NOTE: On re-assembly, ensure that the 'O' ring is carefully
seated within the thermostat phial housing and that the
thermostat phial is inserted carefully to avoid disturbing the
'O' ring.
6.12. DESCALING THE HEATING UNIT
WARNING: ACID/WATER SOLUTION MUST BE USED
WITH EXTREME CAUTION. TAKE CARE NOT TO SPLASH
ONTO SKIN OR INTO THE EYES. WASH ANY AFFECTED
AREAS WITH LARGE AMOUNTS OF COLD WATER AND
SEEK MEDICAL ADVICE.
CARRY OUT THE FOLLOWING OPERATION OUT OF
DOORS. ACID/WATER SOLUTION CAN DAMAGE
FURNISHINGS ETC.
a. Gain general access - see 6.2.
b. Drain the appliance - see 6.6.
c. Remove the heating unit - see 6.11.
d. Invert the heating unit on a suitable bench or table.
e. Using a suitable bung, close off the thermostat phial
pocket.
f. Using rubber tube and acid resisting tanks, assemble
as shown in fig.36.
g. Fill the upper container with a proprietary brand of
descalent or a solution of 10 parts water to 1 part
hydrochloric acid. The water should preferably be hot,
then add ACID to WATER, not water to acid.
h. Adjust the pinch cock and allow the fluid to slowly pass
through the heating unit into the collecting tank.
i. Continue the process until the fluid ceases to bubble. It
may be necessary to replenish the solution.
j. Disconnect and thoroughly wash out the heating unit
with clean water.
Fig. 35
Fig. 36