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a)
central heating mode (Figure 2.3)
The demand for central heating is generated when both the programmer and
the room thermostat are calling for heat. The demand for central heating ceases
if either the programmer or the room thermostat stops calling for heat. Hot water
has priority and therefore if a hot water heating demand is active, a central heating
demand will not be accepted.
When a central heating demand is sensed and accepted, the 3-port diverter valve is
moved to the central heating mode and the pump circulates the water through the
primary circuit and its speed is regulated to maintain the boiler return temperature
measured by sensor, S4, at a pre-set value (60ºC).
The burner ignition sequence will start when the flow temperature measured by
sensor, S4, is below the pre-set limit. Once the burner ignites the fan speed controls
the gas rate to maintain the heating flow temperature at the preset value of 80oC.
When the boiler flow temperature exceeds the preset value, the burner will switch
off and a minimum 4 min delay occurs (an anti-cycle function) before the burner
will automatically relight. During this period, the pump will continue to run.
When the central heating demand ceases, the burner is switched off and the pump
continues to run for a period of 3 minutes pump overrun period. After the pump
overrun period, the pump is switched off and the 3-port diverter valve moves to
the hot water mode.
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Figure 2.3 Central heating circuit
Figure 2.3 Central heating circuit
1. Central heating (CH) flow
4. Cold water (CW) inlet & Filter/Regulator
1. Central heating (CH) flow
7. Hydro -block assembly
-block assembly
4. Cold water (CW) inlet & Filter/Regulator
10. Pump
7. Hydro -block assembly
-block assembly
13. Expansion vessel
10. Pump
16. Venturi assembly
13. Expansion vessel
19. Manual air vent
16. Venturi assembly
22. Flue gas temperature sensor (S2)
19. Manual air vent
25. Spark electrode
22. Flue gas temperature sensor (S2)
25. Spark electrode
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2. Domestic hot water (DHW) outlet
5. Central heating (CH) return
2. Domestic hot water (DHW) outlet
8. 3 port diverter valve assembly
5. Central heating (CH) return
11. Pressure relief valve (PRV)
8. 3 port diverter valve assembly
14. Gas valve
11. Pressure relief valve (PRV)
17. Burner
14. Gas valve
20. DHW temperature & flow sensor (S3)
17. Burner
23. Safety (OHT) sensor
20. DHW temperature & flow sensor (S3)
26. Flame sensing electrode
23. Safety (OHT) sensor
26. Flame sensing electrode
TEcHNIcAL INFOrMATION
2.0
(b)
Domestic hot water mode (Figure 2.4)
Hot water has priority. A hot water demand at any
hot water terminal fitting will override any central
heating demand.
The controller senses the hot water flow by means
of a solid state (S3) flow switch and moves the
3-way diverter valve to the hot water mode. This
allows the pump to circulate the primary water
through the plate heat exchanger.
The burner will light automatically and the
temperature of domestic hot water is controlled by
the DHW flow rate and temperature sensor S3.
When the domestic hot water demand ceases, the
burner will switch off and the diverter valve will
remain in the domestic hot water mode unless
there is a demand for central heating. However
the central heating will not start until a 40 second
delay period has expired.
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Figure 2.4 Domestic hot water circuit
Figure 2.4 Domestic hot water circuit
Figure 2.4 Domestic hot water circuit
Figure 2.4 Domestic hot water circuit
3. Gas inlet
6. Pressure relief valve discharge
3. Gas inlet
9. Plate heat exchanger
6. Pressure relief valve discharge
12. Automatic air vent
9. Plate heat exchanger
15. Fan
12. Automatic air vent
18. Primary heat exchanger
15. Fan
21. Temperature & pressure sensor (S4)
18. Primary heat exchanger
24. Boiler flow temperature sensor (S1)
21. Temperature & pressure sensor (S4)
24. Boiler flow temperature sensor (S1)
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