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Building Technologies
Modular Heating Controller RMH760B
CE1P3133en
HVAC Products
6 Boiler temperature control
05.02.2007
6.6.10 Frost protection for the boiler
The boiler temperature is monitored to ensure frost protection for the boiler.
If the boiler temperature drops below 5 °C, the burner will be switched on.
When the boiler temperature returns to a level above SD (minimum boiler
temperature plus switching differential), the burner will be shut down.
6.6.11 Maintained
boiler return temperature
Minimum limitation of the return temperature shall ensure that, in the area of the boiler
inlet also, the temperature will not drop below the permissible level.
Main menu > Commissioning > Settings > …
or
Main menu > Settings > Boiler > Limitations
Operating line
Range
Factory setting
Boiler return temperature min
---- / 8…140 °C
----
Lock sig maintained boil ret temp
None / Uncritical /
Critical
Critical
In the case of a boiler with the boiler pump connected in series with the boiler, the
maintained boiler return temperature is ensured by reducing the amount of heat drawn
by the heating circuits. The function is activated as soon as a minimum limit value of
the boiler return temperature is set and a return temperature sensor is present.
This function is also available when only a return temperature sensor is configured (that
is, no boiler and no pump). It is intended for use in plants with no direct boiler control.
In a networked system, only one boiler return sensor may be used since its measured
value can generate a locking signal. Locking signals may only have one single source.
313
3S
71
BoPu
TBo
TRtBo
If the boiler return temperature drops below the limit value, a locking signal will be
generated and delivered to all consumers. These will then lower their setpoints or
switch their pumps off (e.g. the storage tank charging pump).
The type of locking signal can be parameterized. The factory setting generates a critical
locking signal. This means that heating circuits, precontrol, DHW charging and, if
present, a system pump would be switched off or reduced.
Setting
Uncritical
(uncritical locking signals) ensures that DHW heating, precontrol,
and the system pump will not be impacted by the maintained boiler return temperature.
For the heating circuits, it can be parameterized whether or not they shall respond to
uncritical locking signals.
It is important to check whether the return temperature sensor is exposed to return
water in all operating states. If, during DHW charging, the return temperature is not
correctly acquired, it must be made certain that the maintained boiler return tempera-
ture will have no impact on DHW heating. Also, the maintained boiler return tempera-
ture must not act on the main pump if the return temperature is only correctly acquired
when the main pump runs.
In the case of a boiler with bypass pump (boiler pump parallel to the boiler), maintained
boiler return temperature can be ensured by activating the bypass pump.
Maintained boiler return
temperature through
lower consumer set-
points
Maintained boiler return
temperature with bypass
pump
