Hamworthy Purewell VariHeat 70c Installation, Commissioning And Servicing Instructions Download

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HAMWORTHY HEATING LTD

PUREWELL

Vari

Heat c

500001169/T

8.3 - Functions

8.3.1 Frost Protection

Note: - to access this function, the circulating pump must be wired to the LMU through a suitable contactor.
There are two levels of frost protection available dependent on the sensor options used.
1st stage - When the boiler water temperature is below 5°C, the burner and the heating pump are switched on.
When the temperature increases and exceeds 15°C, the burner stops and the pump continues for the duration of
the pump overrun.
2nd stage - This additional function uses the outside air temperature (if a sensor has not been fitted, the function
is blocked) and provides three levels of activation.



If the outside temperature is less than or equal to –5°C, the pump operates continuously



If the outside temperature is between –4 & 1.5°C, the pump operates for 10 minutes every 6 hours.



If the outside temperature is greater than 1.5°C, the pump is switched off.

Note:- any demand for dhw is given priority.
Should protection be required for the building fabric, then a QAA73 programmable room sensor must be used to
maintain the internal building temperature.

8.3.2 Anti Legionella

To prevent the development of pathogenic bacteria in the domestic hot water tank during prolonged shut downs or
low storage temperatures, the dhw must be heated once a week to a temperature greater than 60°C.
The anti legionella function heats the dhw once a week on Monday, after the first load, to 65°C.

8.3.3 Pump overrun

When the heating mode ends, the heating circuit pump remains on for a period (depending on the settings used -
QAA73: 544).
In dhw systems, when the dhw heating period ends, the heating pump remains on until the return temperature
drops below 70°C. During this period, the dhw selector valve (if fitted) is in the open position.

8.3.4 Pump or selector valve kick

If either the heating circuit pump or dhw selector valve have not been activated for more than 24hours, then dur-
ing an off period the pump or valve is activated for 5 seconds.

8.3.5 Boiler overheat protection

The boiler flow sensor in combination with the return sensor, provide overheat protection as follows:



If the first level temperature is exceeded, a fault code is displayed.



If the second level temperature is exceeded, an alarm code is displayed and the boiler will switch off. The
boiler must be reset to restart.

To restart the boiler, the temperature must fall, accordingly the fan and pump will continue to operate until the boil-
er heat exchanger temperature drops.
Additionally, should the

∆

T across the boiler heat exchanger exceed 25°C, the burner will reduce output to mini-

mum rate. Should the

∆

T exceed 30°C, the burner will shutdown.

8.3.6 Anti-cycling

Dependent on the installation and the minimum firing rate of the boiler, the control monitors the heating tempera-
ture curve and will hold off a boiler from firing and thus reduce the number of operations.

8.3.7 Automatic summer / winter switching

Note: - This function is only available when an outside sensor is fitted.
The automatic summer/ winter switching function enables the summer mode to be switched to winter mode (vice
versa) throughout the year, without the need for manual intervention.
The heating is shut down when the average outside temperature measured over the preceding 24hours is greater
than 1°C above the set point (20°C).
The heating is automatically started up again when the average outside temperature measured over the preced-
ing 24hours is less than 1°C below the lower limit of the hysteresis threshold of the set point (18°C).
Note: - The switch over setting is set to 19°C and can only be changed using the QAA73 room sensor.
The automatic mode must obviously be activated on the boiler as well as on the QAA73, for the function to oper-
ate. The function is automatically activated by a default setting in the QAA73.