Red boilers and Hydro stoves - System Configurations and operating characteristics

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Introduction

This article describes the operating parameters & characteristics of the circulation pump in the Compact range of boilers, depending on System Configuration setting and boiler operating conditions. It also describes the conditions that the boiler will fire under, based on the method of call (internal probe, external thermostat, or NTC probe) and the temperatures that they are observing versus appliance settings, as may be relevant.


These characteristics vary depending on Configuration (1-5) and whether the boiler is being called to fire or not. The article is set out in sections by System Configuration number.



Glossary

A list of the parameter names used in describing the configuration characteristics follows (not in alphabetical order):


‘Auto Eco’: A function that permits the appliance to switch off into a standby mode a proscribed period of time of running at minimum rate (‘Off Time Eco’) after a demand for heat is satisfied. If Auto Eco is not enabled, the appliance remains burning at minimum rate after a demand for heat is satisfied but does not switch off unless either: A) The internal programmer does so; B) The appliance is manually switched off or; C) The appliance overheats or shuts down due to an alarm condition.


‘Season’: The two options (Winter, Summer) permit the appliance to respond to calls for heat and operate relative to whether the call is from either space heating OR DHW (Winter), or DHW Only (Summer). The options for selecting either Winter or Summer are relative only to Configurations 2 or 3, as these configs. are designed for the appliance to either generate instant DHW via a combi type PHE assembly (this is a pump group option that is Not supplied to the UK market due to concerns about condensing of flue gasses and tarring during DHW production), or to deliver primary heat to an indirect DHW cylinder. When heating a DHW cylinder, in either configuration, the appliance ‘knows’ that the call is for DHW as it comes either from a cylinder thermostat (Config 2.2) or NTC probe (Config. 3), and in turn, will direct the primary heat to the cylinder by controlling a 3-Port diverter valve. It is intended that the end user selects the relevant season dependent on the time of year and the need for space heating or not - the intention being that in ‘Summer’ mode, the appliance cannot respond to the internal probe or connected external room thermostat, or physically deliver heat to the space heating circuit.


'Temp Ambient': This describes the actual ambient temperature in the room that the appliance is installed in. This is relevant when the appliance’s internal temperature probe is active and thus the boiler will respond to it calling for space heat.


`Temp Set Ambient`: This is the target temperature that is set on the appliance for it to heat the room to that it is installed in. This option will only be available in the Set Temperature menu when the internal probe is active and the appliance is set to Configurations 1 - 3.


`Temp H20`: This describes the actual water temperature of the boiler jacket at any given moment; This information is normally shown on the control panel display.


`Set Temp H20`: This is the target temperature that is set on the appliance for it to heat the primary water in the boiler jacket to, and thus to deliver to the space heating circuit / cylinder / buffer as relevant. This option is generally available in the Set Temperature menu when the External Thermostat option is active.


`T On Pump`: This is the set point temperature of the boiler water jacket, that is set on the appliance, for the pump to start circulating, as the jacket temperature rises. This option is available to be adjusted in all configurations. Note that this parameter also works in conjunction with ‘Pump Hysteresis’ - see below.


`Pump Hysteresis`: This parameter defines the temperature at which the appliances pump stops circulating, as the jacket temperature falls from above the value of ‘T On Pump’, to below it. This value is one of the Technical Parameters and its default value is 3°C. So, for example:

IF ‘T On Pump’ = 50°C;

THEN as the jacket temperature increases until it reaches 50°C, at that point the pump starts running. From this point, the pump will now continue to run Until the jacket temperature Falls to: (‘T On Pump’ - ‘Pump Hysteresis’), or (50 - 3) = 47°C


`Pump T Off`: This parameter defines the duration that the pump will continue to run for, following a demand for heat being satisfied. This value is one of the Technical Parameters and its default value is 10 Minutes. This parameter works with respect to both the target & actual water jacket temperatures, and the threshold pump operating temperature - which if it is met, overrides the running duration.


`T Cylinder`: This describes the actual temperature of the DHW in a cylinder at any given moment - this reference being valid only when in Configuration 3 where the value from an NTC probe in the DHW cylinder, & connected to the boiler, is displayed on the control panel.


`T Set Cylinder`: This is the target temperature that is set on the appliance for it to heat the DHW in a cylinder to. This option is available in the Set Temperature menu when an NTC probe in the DHW cylinder is connected to the boiler and the appliance is set to Configuration 3.


`Temp Buffer`: This describes the actual temperature of the primary water in a buffer tank or thermal store at any given moment - this reference being valid only when in Configuration 5 where the value from an NTC probe in the buffer / store, & connected to the boiler, is displayed on the control panel.


`T Set Buffer`: This is the target temperature that is set on the appliance for it to heat the primary water in a buffer tank or thermal store to. This option is available in the Set Temperature menu when an NTC probe in the buffer / store is connected to the boiler and the appliance is set to Configuration 5.


NOTE: In all the ‘Thermostat Operation’ scenarios described for Configurations 1 - 3, the operation is described in terms of the boiler’s internal (ambient) probe as the control. If however an external thermostat is used, the boiler simply responds to the contacts on the thermostat calling - there is no reference to a setpoint temperature on the appliance settings. For Configurations 3 and 5, where an NTC sensor is used, then a setpoint temperature Is referenced - see the relevant section below.



Configurations

Configuration 1

This configuration is intended for installations where the appliance is connected directly to a space heating circuit only and is called for heat either by the internal probe or an external room thermostat.

Auto Eco:


Off (can be enabled)


Season:

‘Winter’ enabled (‘Summer’ cannot be enabled)
Thermostat:


Internal boiler probe enabled (External Thermostat can be enabled)
Thermostat operation (Internal Probe):


  • If ‘Temp Ambient’ = ‘Temp Set Ambient’, then Demand is Satisfied.
  • If ‘Temp Ambient’ <= (‘Temp Set Ambient’ - 0.5°C), the Call for Heat.


During demand:


  • Pump is On if ‘Temp H20’ > ‘T On Pump’
  • Pump is Off if ‘Temp H20’ < (‘T On Pump’ - ‘Pump Hysteresis’)


When Demand Satisfied:


  • Pump remains on for ‘Pump T Off’ IF ‘Temp H20’ > ‘T On Pump’
  • If During ‘Pump T Off’: ‘Temp H20’ < (‘T On Pump’ - ‘Pump Hysteresis’);
    Then: Pump is Off.
    Else: After ‘Pump T Off’, Check temp; If ‘Temp H20’ > (‘Set Temp H20’ - ‘Pump Hysteresis’) then Pump is On Until ‘Temp H20’ <= (‘Set Temp

H20’ - ‘Pump Hysteresis’).


Configuration 2

There are two intended scenarios that would use this configuration:


  • Boiler is fitted with instant DHW pump/plate kit and links to space heating circuit, called by internal probe or external room thermostat. (This configuration is Not sold in the UK and Is Not recommended).
  • Boiler links to DHW cylinder and to space heating circuit via 3-Port diverter valve, controlled by boiler to give DHW Priority (W-Plan). Cylinder thermostat wires to Instant DHW flow switch position on motherboard; Space heating circuit called by internal probe or external room thermostat.

In either scenario, the boiler will respond in a normal fashion to calls for heat from the internal probe/external thermostat. When a call for DHW is made, the boiler will modulate to full power and use a special set of parameters that generate extra heat/power during the demand. In scenario 2), the 3-Port valve will default to the space heating circuit, but will move to DHW position during a DHW call.


Auto Eco:


Off If ‘Winter’ mode (can be enabled); On If ‘Summer’ mode (cannot be deactivated).


Season:


‘Winter’ enabled (‘Summer’ can be enabled)


Thermostat:


Internal boiler probe enabled (External Thermostat can be enabled)


Thermostat operation (Internal Probe):


‘Winter’ enabled:
  • If ‘Temp Ambient’ = ‘Temp Set Ambient’, then Demand is Satisfied.
  • If ‘Temp Ambient’ <= (‘Temp Set Ambient’ - 0.5°C), then Call for Heat,
    AND 3-Port Valve diverts to Space Heating.
  • If DHW Cylinder stat Calls, 3-Port Valve diverts to DHW
    AND IF Auto Eco = Enabled, boiler restarts immediately if shutdown in Auto Eco.



‘Summer’ enabled:
  • Internal Probe and External Thermostat are Deactivated;
  • Auto Eco is Enabled (cannot be deactivated);
  • 3-Port valve Always diverts to DHW.


During Demand:


  • Pump is On if ‘Temp H20’ > ‘T On Pump’
  • Pump is Off if ‘Temp H20’ < (‘T On Pump’ - ‘Pump Hysteresis’)


When Demand Satisfied:


  • Pump remains on for ‘Pump T Off’ IF ‘Temp H20’ > ‘T On Pump’
  • If: During ‘Pump T Off’: ‘Temp H20’ <(‘T On Pump’ - ‘Pump Hysteresis’);
    Then: Pump is Off
  • Else: After ‘Pump T Off’, Check temp;
  • If ‘Temp H20’ > (‘Set Temp H20’ - ‘Pump Hysteresis’) then

Pump is On Until ‘Temp H20’ <= (‘Set Temp H20’ - ‘Pump Hysteresis’).


Configuration 3

This configuration is similar to that described above in Config. 2.2, i.e. Boiler links to DHW cylinder and to space heating circuit via 3-Port diverter valve, controlled by boiler to give DHW Priority (W-Plan). The difference is for the DHW controls:


  • Cylinder NTC probe wires to terminals 3-4 on rear of boiler;
  • Space heating circuit called by internal probe or external room thermostat.


Auto Eco:


Off If ‘Winter’ mode (can be enabled); On If ‘Summer’ mode (cannot be deactivated).


Season:


‘Winter’ enabled (‘Summer’ be activated)


Thermostats:


Internal boiler probe enabled (External Thermostat can be enabled) for Space Heating: NTC Sensor in DHW cylinder for DHW call.


Thermostat operation (Internal Probe):


‘Winter’ enabled:
  • If ‘Temp Ambient’ = ‘Temp Set Ambient’, then Demand is Satisfied.
  • If ‘Temp Ambient’ <= (‘Temp Set Ambient’ - 0.5°C), then Call for Heat.
    AND 3-Port Valve diverts to Space Heating.
  • If DHW NTC Calls, 3-Port Valve diverts to DHW.
‘Summer’ enabled:
  • Internal Probe and External Thermostat are Deactivated;
  • Auto Eco is Enabled (cannot be deactivated);
  • 3-Port valve Always diverts to DHW.


During Demand:


  • DHW is Calling IF cylinder temp <= ‘T Set Cylinder’ + 0.5°C
    THEN: ‘Set Temp H20’ changers to ‘Set Temp DHW’
  • IF DHW NTC is Calling:
    Pump is On if ‘Temp H20’ > (‘T Cylinder’ + 3°C)
    Pump is Off if ‘Temp H20’ < (‘T Cylinder’ + 1.5°C)



  • DHW is Satisfied if cylinder temp = ‘T Set Cylinder’ + 2.5°C
    THEN: Pump is On if ‘Temp H20’ > ‘T On Pump’
    Pump is Off if‘ ‘Temp H20’< ‘T On Pump’


When Demand Satisfied:


  • Pump remains on for ‘Pump T Off’ IF ‘Temp H20’ > ‘T On Pump’
  • If: During ‘Pump T Off’: ‘Temp H20’ <(‘T On Pump’ - ‘Pump Hysteresis’);
    Then: Pump is Off.
  • Else: After ‘Pump T Off’, Check temp;
  • If ‘Temp H20’ > (‘Set Temp H20’ - ‘Pump Hysteresis’) then

Pump is On Until ‘Temp H20’ <= (‘Set Temp H20’ - ‘Pump Hysteresis’).

Configuration 4

This configuration is intended for installations where the appliance is connected to a buffer tank or thermal store, which in turn delivers heat to space heating and DHW zones. The tank/store calls for heat by a cylinder thermostat.


Auto Eco:


On (cannot be deactivated)

Season:


‘Winter’ enabled (‘Summer’ cannot be enabled)

Thermostat:


  • Internal boiler probe deactivated - cannot be enabled.
  • External Thermostat enabled - cannot be deactivated.
  • NTC Probe deactivated - cannot be enabled.

Thermostat operation:


  • 3-Port Valve Always directs to Space Heating (If Connected)
  • ‘Set Temp H20’ is 80° (can be altered)
  • Buffer Thermostat contacts ‘Make’: Call for Heat.
  • Buffer Thermostat contacts ‘Break’: Demand Satisfied.

During Demand:


  • Pump is On if ‘Temp H20’ > ‘T On Pump’
  • Pump is Off if ‘Temp H20’ < (‘T On Pump’ - ‘Pump Hysteresis’)

When Demand Satisfied:


  • Pump remains on for ‘Pump T Off’ IF ‘Temp H20’ > ‘T On Pump’
  • If: During ‘Pump T Off’: ‘Temp H20’ <(‘T On Pump’ - ‘Pump Hysteresis’);
    Then: Pump is Off.
  • Else: After ‘Pump T Off’, Check temp;
  • If ‘Temp H20’ > (‘Set Temp H20’ - ‘Pump Hysteresis’) then

Pump is On Until ‘Temp H20’ <= (‘Set Temp H20’ - ‘Pump Hysteresis’).


Configuration 5

This configuration is intended for installations where the appliance is connected to a buffer tank or thermal store, which in turn delivers heat to space heating and DHW zones. The tank/store calls for heat by an

NTC sensor.

Auto Eco: On (cannot be deactivated)

Season: ‘Winter’ enabled (‘Summer’ cannot be enabled)

Thermostat:

  • Internal boiler probe And External Thermostat deactivated - cannot be enabled.
  • NTC Probe Enabled.

NTC Operation:

  • 3-Port Valve Always directs to Space Heating (If Connected)
  • ‘Set Temp H20’ = (‘T Set Buffer + 10°C)
  • IF ‘Temp Buffer’ <= (‘T Set Buffer - 0.5°C) THEN Call for Heat.
  • IF ‘Temp Buffer’ > (‘T Set Buffer + 0.5°C) THEN Demand Satisfied.

During Demand:


  • Pump is On if ‘Temp H20’ > (‘Temp Buffer’ + ‘Pump Hysteresis’)
  • Pump is Off if ‘Temp H20’ < ‘Temp Buffer’

When Demand Satisfied:


  • Pump is On if ‘Temp H20’ > (‘Temp Buffer’ + ‘Pump Hysteresis’)
  • Pump is Off if ‘Temp H20’ < ‘Temp Buffer’