Bosch TRONIC 5000C Pro Reference manual

Technical Service Bulletin:
Triac Printed Circuit Board Replacement
TRONIC 5000C Pro Models: WH17, WH27, WH36
Introduction
WARNING
ELECTRICITY IS EXTREMELY DANGEROUS.
TAKE EXTRA PRECAUTIONS AND ENSURE ALL
CIRCUIT BREAKERS ARE OFF BEFORE
PERFORMING ANY WORK ON THE HEATER
WARNING
THE FOLLOWING PROCEDURE MUST BE
PERFORMED BY A LICENSED ELECTRICIAN
Tools Required
Electrical meter
Phillips head screwdriver
Small flat head screwdriver
Heat sink paste
Replacement of the triac printed circuit board will be
easier if you can work slightly above the unit.
Preparation
1. Remove the four cover screws and retain, lift off the cover and
store safely.
2. Using an electrical meter, confirm power is off the the heater.
Removing the triac wiring
1. Remove the thin white signal wires from the printed circuit
boards by gently bending the locking tab on the connector with
a small flat head screwdriver so that the plug can be removed
(Fig. 1). These cables can be moved out of the working area.
Fig. 1
2. Using the small flat head screwdriver pull the ¼" push on
connectors off the triac printed circuit boards (Fig. 2). The
recommended method is to use a small flat head screwdriver in
the rectangular hole and then push the screwdriver blade so that
the connector pulls off straight.
Fig. 2

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2 | Triac Printed Circuit Board Replacement
3. The wiring back to the main terminal block and element can be
placed out of the working area.
On the 36kW the triac printed circuit board on the right
hand assembly uses ring terminals retained by large
screws. These can be removed with a Phillips head
screwdriver, retain the screws and washers for
reassembly.
Removing the printed circuit boards
1. Using a Phillips head screwdriver undo the one or two triac
clamping screws (Fig. 3 & 4). Using a magnetic bit will make this
easier as the screws and washers will lift out easily (Fig. 5).
Retain these screws and washers for refitting.
The white paste on these parts is normal and is used
to transfer heat from the triac to the brass head. Avoid
getting it onto clothing and wipe / wash from hands
before eating or drinking.
Fig. 3
Fig. 4
27kW & 36kW
Only
Fig. 5
2. Using the small flat head screwdriver, gently open the latch on
the moulding holding the printed circuit board in place (Fig. 6).
Fig. 6
Latch
Dual triac printed circuit board
all models
3. Rotate the printed circuit board slightly to clear the latch and
remove from the slot at the other end (Fig. 7). Discard the
printed circuit board in accordance with the local environmental
laws.
Fig. 7
Single triac printed circuit
board 27kW & 36kW only
Latch

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Triac Printed Circuit Board Replacement | 3
Refitting the circuit boards
1. Lay the new printed circuit board on a work surface. Using the
syringe or small packet supplied squeeze a small amount of
white heat transfer paste onto the metal underside of each of
the triac switches (Fig. 8). This should be approximately the size
of the head of the triac fitting screw (¼” diameter).
WARNING
AN INADEQUATE AMOUNT OF HEAT SINK PASTE
CAN LEAD TO TRIAC FAILURE AND OVERHEATING,
CAUSING THE THERMAL CUT-OUT TO TRIP.
Fig. 8
2. Reassemble the printed circuit boards to the moulding by
slotting in one end and then rotating clockwise to click into the
latch on the moulding (Fig. 9 & 10).
Fig. 9
Dual triac printed circuit board
Slot in here
Snap in here
Fig. 10
Single triac printed circuit board
Slot in here
Snap in here
3. Using the Phillips head screwdriver (ideally with a magnetic bit)
insert the screw with lock washer through each of the triac
switches and lightly engage the thread (Fig. 3 & 4). Insert all
screws (1 or 2) before tightening hand tight without damaging
the screw head.
WARNING
INADEQUATE CONTACT BETWEEN THE TRIAC
BASE AND THE BRASS HEATING ELEMENT
ASSEMBLY CAN LEAD TO TRIAC FAILURE.
ENSURE ALL SCREWS ARE TIGHT AND CONTACT
IS SUFFICIENT (SEE FIG. 11).
Fig. 11

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4 | Triac Printed Circuit Board Replacement
Reconnecting the wiring
1. Refer to the wiring diagram for each model. Refitting of the ¼”
connectors (Fig. 2) should be done by pushing them straight
onto the tabs on the printed circuit board. Use a flat blade
screwdriver to push the connectors on if required after aligning
for straight engagement.
2. Assemble the wiring to the printed circuit board nearest the
metalwork first for ease of access (Fig. 12 - 16).
Fig. 12
17kW & 27kW
Brown terminal block wire
Left hand assembly– Short Blue element wire
Right hand assembly– Short Black element wire
Left hand assembly – Blue terminal block wire
Right hand assembly– Black terminal block wire
Short Brown
element wire
Fig. 13
27kW only
Short Grey element wire
Grey terminal
block wire
Fig. 13
27kW only
Short Grey element wire
Grey terminal
block wire
Fig. 14
Grey terminal
block wire
Short Grey
element wire
36kW Only Left hand assembly – Short Blue element wire
Center assembly – Short White element wire
Right hand assembly – Short Black element wire
Left hand assembly – Blue terminal block wire
Center assembly – White terminal block wire
Right hand assembly – Black terminal block wire
Fig. 15
36kW center & left assemblies
Brown terminal block wire
Short Brown element wire
Fig. 16
Brown terminal block wire
36kW right assembly
Short Brown element wire

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5 | Triac Printed Circuit Board Replacement
Bosch Thermotechnology Corp.
50 Wentworth Avenue
Londonderry, NH 03053
Tel: [phone]
Fax: [phone]
www.bosch-climate.us
3. Reconnect the thin white signal wires; the three wire connector
goes to the printed circuit board mounted nearest the back. The
two wire cable goes to the printed circuit board on the left hand
side of the head on the 27kW & 36kW units.
Ensure the connector is aligned with all of the the pins
and not offset or the heater will not work properly.
Refitting the cover
1. Before refitting the cover perform a once over check:
Are all connections made correct to the wiring diagram for
this model?
Are all connections tight?
Is there evidence of the heat transfer paste being squeezed
out from under each of the triac switches where they have
been clamped?
2. Refit the cover using the 4 screws ensuring that no wires are
trapped and that the red clip in lens is not knocked out.
3. Fill the unit with water and follow the commissioning routine in
the user handbook. Ensure you have a continuous flow of water
from all the hot water faucets before resetting the breakers.
WARNING
DO NOT TURN ON THE ELECTRICITY UNTIL THE
UNIT IS FULL OF WATER AS THIS WILL DAMAGE
THE UNIT.