Technical data

ManualsBrandsVOKERA ManualsHeating SystemLinea

Linea 24 & 28

SECTION 2 DESIGN PRINCIPLES AND OPERATING SEQUENCE

2.1 Fig.1 illustrates the general layout of compo-

nents. Fig.2 illustrates the operating principles

described below.

2.2 Central Heating Mode

2.2.1 When the various switches and controls im-

pose a demand for heat, the pump is started.

If the primary pressure is sufficient, the elec-

tronic circuitry is energised. The fan is started,

the gas valve is energised at an intermediate

rate and the electronic ignition goes through

an ignition attempt.

2.2.2 The burner ignition is checked by the elec-

tronic circuitry to ensure correct ignition of the

burner; once successful the gas will flow at

75% of maximum heat input for a period of

approximately 15 minutes and then go to

maximum heat input to maximise heating per-

formance, unless the boiler nears optimum

temperature where it will modulate down to

suit system load.

2.2.3 As water temperature increases this is sensed

by the temperature sensor on the primary heat

exchanger which modulates the burner to

match the heat output to the heat requirement

of the system.

2.2.4 Depending on the load, either a) The water

temperature will continue to rise and the burner

will continue to modulate down; The burner

will switch off at maximum temperature, or b)

the water temperature will fall; the burner

will return to a higher output to match demand.

2.3 Domestic Hot Water Mode

2.3.1 The appliances incorporate a hot water preheat

facility. The appliance will therefore ignite

periodically to maintain heat within the appli-

ance.

2.3.2 The appliance will operate in domestic hot

water mode whenever the mode selector switch

is on regardless of mode selector switch

position and any demand for central heating.

2.3.3 The diverter valve will automatically energise

into the hot water position after central heating

demand, or will stay in the hot water position

after hot water demand. Opening a draw off

tap will energise the pump and fan sending

primary water to the domestic hot water heat

exchanger.

2.3.4 Temperature control is transferred to the do-

mestic hot water thermostat (potentiometer)

which modulates the burner output between

high and low flame to maintain an average

heat input to suit the dhw output required.

2.3.5 An overrun is incorporated in the boiler in both

c/h & dhw modes. The fan overruns until the

boiler water cools to approximately 80°C

(176°F).

2.4 Safety Devices

2.4.1 In both central heating and hot water modes

safe operating is ensured by:

A. Differential pressure unit in the primary

circuit which prevents burner operation if water

pressure is too low.

B. An electronic device that checks the pri-

mary pressure unit for activation. Failure re-

sults in deactivation of the pump, after ap-

proximately 10 minutes of operation.

C. A safety thermostat, which interrupts the

control circuit shutting off the gas valve. At the

same time the fan will still operate.

D. A Pressure differential switch in the flue

system to check the fan's operation before

allowing ignition.

2.4.2 A safety valve is provided to relieve excess

pressure from the primary circuit.

2.4.3 Frost Thermostat

The appliance has a built in frost protection

circuit. Should the boiler temperature sensed at

the primary thermistor fall below 5°C, the boiler

will operate in central heating mode and continue

to operate until the primary thermistor reaches

approximately 40°C.

KEY:

A Central Heating Return.

B Central Heating Flow.

C Hot Water Outlet.

D Cold Water Inlet.

NOTE: pressure switch. Senses water pressure in the

primary circuit and operates the pressure switch

(22)

Fig. 2

Air Intake

Flue Outlet

AB CD

NOTE