tekmar 270 Boiler Control - Manual (Page 11)

11 of 24 © 2010 D 270 - 08/10
DHW Mode 1 - DHW in Parallel no Priority
When a DHW Demand is present, the DHW Pmp / Vlv contact
(terminals 7 and 8) closes. The primary pump contact does not turn
on, but may operate based on a boiler demand.
DHW Mode 2 - DHW in Parallel with Priority
When a DHW Demand is present, the DHW Pmp / Vlv contact
(terminals 7 and 8) closes and the primary pump contact is opened.
DHW Mode 3 - DHW in Primary / Secondary no Priority
When a DHW Demand is present, the DHW Pmp / Vlv contact
(terminals 7 and 8) is closed and the primary pump contact is closed.
This mode can be used if DHW tank is piped in direct return and a DHW
valve is installed.
DHW
Pump
Primary
Pump Boiler
Pump
DHW
Pump
Primary
Pump Boiler
Pump
DHW
Pump
Primary
Pump Boiler
Pump
DHW Mode 4 - DHW in Primary / Secondary with Priority
When a DHW Demand is present, the DHW Pmp / Vlv contact
(terminals 7 and 8) is closed and the primary pump contact is closed.
Priority can only be obtained using external wiring. During a priority
override, the DHW Pmp / Vlv contact is opened until the heating
system has recovered before returning to DHW operation.
This mode can be used if a DHW tank is piped in direct return and
a DHW valve is installed.
DHW MODE 4
External Priority
Interlock
Power to External
Boiler Zones
N.C.
L
DHW
Pump
N
N.O.
L
N
COIL
Power from
DHW Pump / Vlv
Contact
DHW PRIORITY OVERRIDE
The DHW Priority Override applies to DHW modes 2 and 4. To prevent
the building from cooling off too much or the possibility of a potential
freeze up during DHW priority, the control limits the amount of time
for DHW priority. As the outdoor air temperature becomes colder, the
length of time that the control provides DHW priority is reduced. Once
the allowed time for priority has elapsed, the control overrides the DHW
priority and resumes space heating.
To provide external DHW priority, the space heating zones must be
interlocked with the DHW Pmp / Vlv contact. During demands, the
DHW Pmp / Vlv
contact must remove any power to all space heating
zone valves or zone pumps.
Increasing Air Temperature
Incr
easing Time
DHW priorit
y demand time limit
Outdoor Air Temperature
DHW Priority Override DHW Priority Override
DHW
Pump
Primary
Pump Boiler
Pump
Disable
Using External
Wiring