High Limit Safety Cut-Out; Measures For Reducing Tar Deposits - Viessmann VITOTRANS 353 Operating Instructions Manual

Boiler operation
Measures to be carried out in the event of the...

High limit safety cut-out

The high limit safety cut-out is part of the boiler. It is
located behind the programming unit under the front
top panel.
Note
Any high limit safety cut-out response requires a man-
ual reset.
Triggering the function:
The high limit safety cut-out will respond if the boiler
water temperature exceeds 95 °C.
The fan on the boiler is shut down and the air dampers
are closed. This reduces boiler output and lowers the
flow temperature. Boiler overheating is prevented.
Cancelling the function:
Note
The high limit safety cut-out can only be reset
(unlocked) once the boiler water temperature has
reached approx. 70 °C.
!
Please note
If this function is not reset (unlocked), it inhibits
the safety equipment function and can result in
system damage.
Always carry out the following steps.
A
Fig. 13

Measures for reducing tar deposits

Tar deposits in the hopper are caused by condensation
of wood gases on the water-cooled walls. Since the
condensation temperature of the gases is far higher
than the achievable boiler water temperature, tar
deposits are unavoidable. The deposits do not impair
the function of the boiler. Only remove the dry and flak-
ing deposits before heat-up (see page 47).
18
(cont.)
1. Slide the cover on the programming unit to the
right.
2. Press green button
out. A quiet "click" will be audible. The high limit
safety cut-out has been reset.
3. Close the programming unit cover.
4. Acknowledge the excess temperature on the pro-
gramming unit of the control unit with
Note
If the high limit safety cut-out responds several times
within a short period, check the cause. Check whether
the system can absorb any more heat. Notify your
heating contractor.
You can reduce tar deposits by taking the following
steps:
Only use dry fuel: stored for at least 2 years, max.
■
15 % - 20 % moisture content (see page 10).
Heat with as high a boiler water temperature as pos-
■
sible.
■ Maintain a min. return temperature of 65 °C.
■ Recharge or heat up according to demand. Longer
partial load operation increases tar deposits. For
recharging, see page 16.
on the high limit safety cut-
A
d .