Product Overview

© 2012 A 274 - 01/12 2 of 8
Electrical
Application A 274-2
System Description: The Boiler Control 274 controls two On/Off boilers to provide outdoor reset for the space heating
zones. The boilers are piped in reverse return, parallel primary-secondary and the boiler pumps are controlled by the 274 to
allow post purging of the boilers after they have shut off. The 274 also controls a DHW pump. This system can provide DHW
priority over space heating to provide faster DHW tank recovery.
Mechanical
Concept Drawing: This is only a concept drawing, not an engineered drawing. It is not intended to describe a complete system, nor any particular system. It is up to the
system designer to determine the necessary components for and configuration of the particular system being designed, including additional equipment, isolation relays
(for loads greater than the control’s specified output ratings), and any safety devices which in the judgement of the designer are appropriate, in order to properly size,
configure and design that system and to ensure compliance with building and safety code requirements.
S2
S1
P4
P1 P2
P3
A1
A2
120 V (ac)
274
S1 = Outdoor Sensor 070
S2 = Boiler Supply Sensor 082
A1 = DHW Aquastat
A2 = High Limit Aquastat
P1 & P2 = Boiler Pumps
P3 = Primary Pump
P4 = DHW Pump
S2
Boiler
1
S1
6
DHW
5 4
Sup
3
+
2
-
1
Do not apply power
274
N
720
Power
L
8
tN4 Com Out Boil Com BRet/ Relay
1
910
Relay
2
11 12
Relay
3
13 14
Relay
4
15 16
C.A./
Alert
21 22
Boiler
Demand
23 24
DHW
/Setp
Com
Dem
25
Pr.
Dem
19
Prim
P1
18
DHW
/P2
17
P1 P2 P3
C
24V(ac)
R
N
115 V (ac)
Class 2
Transformer
L
A1
A2
Boiler
2
P4
Demands
Setback
Off
EMS
Rotate
Fixed Last
Pump Sequencer
Exercise
Off
Fixed Lead
First On / Last Off
First On / First Off
274 Switch Settings:Essential Control Settings:
Mode = 2