The Vokèra Maxim is a high-efficiency combi boiler designed for domestic heating and hot water systems. It is available in two models, Maxim 25 and Maxim 29, with respective Gas Council (G.C.) numbers 47-364-31 and 47-364-32. The boiler is room-sealed and fan-flued, suitable for internal wall mounting applications only, and operates on a sealed system, not open-vented systems. It complies with various European Directives including Gas Appliance, Yield, Electromagnetic Compatibility, Low-Voltage, Ecodesign, and Energy Labelling Regulations.
Function Description:
The Maxim boiler provides heated water for radiators (central heating) and domestic hot water (DHW) taps. It features electronic ignition, eliminating the need for a pilot light. The central heating is controlled via a time clock and any installed thermostats. The boiler activates when there's a request from the time clock, a thermostat, or when a hot water tap is opened. In case of a fault, the gas supply to the burner is automatically terminated.
Key Components:
The boiler incorporates a fully integrated electronic control board with electronic temperature control, anti-cycle control, pump over-run, self-diagnostic fault indicator, and full air/gas modulation. Other principal components include an aluminium heat exchanger, electronic ignition with flame supervision, a high-head pump, a fan, an expansion vessel, a water pressure switch, a flue sensor, a pressure gauge, and a safety valve.
Operating Modes:
- At Rest: When there are no heating or hot water requests, the frost-protection system and anti-block function are active. The frost-protection system protects the appliance from frost damage in both CH and DHW lines, activating the burner and/or pump if temperatures drop below 5°C (to reach 35°C for CH and 55°C for DHW). The anti-block function energizes the pump and diverter valve actuator for short periods if inactive for over 24 hours.
- Heating Mode: Upon a heat request, the pump and fan start, and the fan speed modulates until the correct signal voltage is received by the control PCB, initiating an ignition sequence. After successful ignition, the gas rate increases to 75% for 15 minutes, then modulates to suit the set requirement. The burner shuts down when the desired temperature is reached, followed by a three-minute anti-cycle delay. The pump and fan may continue to operate to dissipate residual heat.
- Hot Water Mode: When a DHW tap is opened, the pump and fan start, and the fan speed modulates. An ignition sequence is enabled, and after successful ignition, the gas rate increases to maximum or modulates to stabilize the temperature. The burner shuts down if the desired temperature is exceeded. The pump and fan may continue to operate to dissipate residual heat.
Safety Devices:
The Maxim boiler is equipped with several safety devices to ensure safe operation:
- A water pressure switch monitors system pressure and de-activates the pump, fan, and burner if pressure drops below tolerance.
- A fan speed sensor ensures safe burner operation.
- A high limit thermostat overrides temperature control to prevent or interrupt burner operation.
- A flame sensor shuts down the burner if no flame signal is detected.
- A flue sensor.
- A safety valve releases excess pressure from the primary circuit.
Important Technical Specifications:
| Feature |
Maxim 25 |
Maxim 29 |
| Height |
715 mm |
715 mm |
| Width |
405 mm |
405 mm |
| Depth |
250 mm |
250 mm |
| Dry weight |
27 kg |
28 kg |
| CH Heat Input |
20.00 kW |
25.00 kW |
| CH Max Output (60/80°C) |
19.50 kW |
24.45 kW |
| DHW Heat Input |
25.00 kW |
29.00 kW |
| DHW Flow Rate (ΔT35°C) |
10.20 l/min |
11.9 l/min |
| Inlet Pressure (G20) |
20.0 mbar |
20.0 mbar |
| Expansion Vessel Capacity |
8 litres |
8 litres |
| Electrical Supply |
230V/50Hz |
230V/50Hz |
| Internal Fuse |
3.15A T |
3.15A T |
| External Fuse |
3A |
3A |
| SEDBUK Efficiency |
90.0% |
90.2% |
| NOx Rating |
Class 6 |
Class 6 |
Clearances Required:
- Above: 150 mm
- Below: 150 mm
- Left Side: 12 mm
- Right Side: 12 mm
- Front: 600 mm
Flue Details (Concentric 60-100):
- Max Horizontal Flue Length: 5.85m (Maxim 25), 4.85m (Maxim 29)
- Max Vertical Flue Length: 6.85m (Maxim 25), 5.85m (Maxim 29)
- Reduction for each 45° bend: 1.0 metre
- Reduction for each 90° bend: 1.0 metre
Usage Features:
- Controls: The appliance controls are located on the lower front and include a pressure gauge, mode selector, temperature selectors (for CH and DHW), burner ON (green LED), fault indicator (red LED), DHW pre-heat/servicing mode indicator (yellow LED), and an optional integral time clock/programmer.
- Temperature Adjustment: CH temperature can be adjusted from 40°C to 80°C. DHW temperature can be adjusted from 37°C to 60°C.
- DHW Pre-heat Function: Activated by turning the DHW temperature adjustment knob to the symbol, indicated by the yellow LED. This function keeps water in the DHW exchanger hot to reduce standby times.
- Automatic Temperature Control (SARA): When the CH temperature selector is set within sectors 5 and 7, the boiler automatically adjusts the heating temperature. This is visualized by the green LED blinking.
- System Pressure: The pressure gauge should read between 1 and 1.5 BAR when the boiler is off and cooled. Minimum permissible level is 0.5 BAR.
- Resetting: If the red fault LED is illuminated, the appliance requires manual reset. Allow two minutes before rotating the mode selector knob to the OFF/standby position.
- Shut Down: For short periods, turn the time clock to off. For long periods, drain the system, and turn off gas, water, and electricity supplies.
Maintenance Features:
- Annual Servicing: It is recommended that the boiler be checked and serviced at regular intervals (generally once per year) by a competent person. This ensures continued safe and efficient operation.
- Condensate Trap: During normal operation, the boiler produces condensate collected in a trap. The flexible condense outlet pipe must be connected to a plastic waste pipe with a minimum 3° fall towards the drain. The trap should be checked and cleaned during servicing.
- System Flushing: The heating system must be flushed both cold and hot during commissioning and after maintenance, using a cleanser suitable for Aluminium heat exchangers.
- Inhibitors: Vokèra recommends using an inhibitor suitable for aluminium heat exchangers to protect the boiler and system from corrosion. Water treatment should be in accordance with BS 7593 and DWTA code of practice.
- Component Removal: Procedures for removing various components such as the pump assembly, safety valve, air release valves, water pressure switch, thermistors, PCB, gas valve, electrodes, flue fan & mixer, burner, main heat exchanger, automatic by-pass & DHW non-return valve, expansion vessel, and condense trap are detailed in the manual.
- Gas Tightness Check: A gas tightness check must be carried out if any gas-carrying components have been removed or disturbed.
- CO2 and Gas Valve Adjustment: The gas valve must be set up or adjusted with a properly calibrated flue gas analyser. The boiler has a CO2 function mode for combustion analysis.
- Electrical Checks: Electrical checks (earth continuity, short circuit, polarity) must be carried out by a suitably qualified person during installation and servicing.
Status Indicators:
- Green LED: Indicates flame presence, boiler working/responding to a heating/hot water request.
- Red LED: Indicates a fault and failed-safe condition.
- Yellow LED: Indicates DHW pre-heat function working or servicing operation in progress.
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