Central heating is produced from the following models, but in a slightly different way according to type and requiring some variations in their individual plumbing requirements.

Heatranger Solid-Fuel models 216SFW & 355SFW

Direct, Sealed or un-vented systems must not be used with these models

With these models it is normal installation practice to pump-assist the central heating circuit, whilst retaining gravity circulation for the domestic hot water pipe-work.

The heating pipe-work should be a two-pipe, small bore system with the radiators having the appropriate control valves and lock-shield valves for balancing. The control valves may be thermostatic, but it is recommended that at least one radiator should remain in operation with a manual valve, to serve as a heat-leak

An injector tee (supplied with the Rayburn) must be fitted as shown, to ensure that the gravity hot water circulation continues even when the pump is in operation. Note the correct position for this fitting. Drain-cocks should be fitted at the lowest points of the system.

The system must be fully flushed through and filled with an appropriate corrosion inhibitor

Since radiator sizes and outputs vary considerably, it is not possible to quote the actual number of radiators that can be served by each model. It is more appropriate to refer to the radiator manufacturer's rated output and to match this to the Rayburn's specification. Solid fuel appliances often have their boiler central heating rating expressed as being able to heat a specific surface area of radiator, but it must be remembered that radiators have at least 2 sides, whilst double radiators have 4. Convector radiators with fins also increase the surface area and thus the input demand. Allow 10% for pipe-work heat losses.

The available heat to radiators and pipes from these models (in addition to domestic hot water) is:-

• These figures are average over a 2 hour period to allow for the re-fuelling and recovery cycle.
• Control over the central heating is normally achieved by switching the circulating pump, using a time-clock and/or room thermostat.
• In the case of the Rayburn 355SFW, when the pump starts on demand for heating, the water temperature in the Rayburn will fall and this will be recognized by it's own thermostat. This will react by opening the air supply to the fire and thus increasing the burning rate.
• A suggested method of wiring the pump is given below. In each case, a low temperature thermostat isolates the pump when the firebox temperature falls below 50 deg C, thereby reducing corrosion from condensation if the fire is idling.
• A pipe thermostat should also be fitted to the flow pipe adjacent to the Rayburn, which will switch the pump on to prevent boiling of the domestic hot water, if the temperature exceeds about 80 deg C.

To prevent the possibility of the radiators becoming warm from gravity circulation when the pump is off, it is good practice to fit a check valve or motorised zone valve as shown in the diagram. In the latter case this should be wired in parallel to the pump.

The system must be installed in accordance with local water bylaws, Building Regulations and standards and we strongly encourage that the plumbing be carried out by a competent person.

Heatranger Gas-fired Models 480AL CF & 480AG CF

• These models offer considerable flexibility in central heating system design and are compatible for use with most modern systems.
• This can include normal open-vented or sealed systems utilizing conventional radiators or underfloor heating. They may be also used in conjunction with 'Heatstore' type hot-water cylinders.
• Both models can have their boiler outputs range-rated between 17.6kW and 23.4 kW, by simply adjusting the relevant burner gas pressure.
• Whilst it is difficult to predict the total number of radiators which can be supplied, it is more appropriate to refer to the radiators stated output and then check that the total is within the maximum output of 23.4kW. Always allow a margin of 10% for pipe-work losses and of course an allowance for the domestic hot water requirements. Thermostatic radiator valves (Trv's) may be used.
• A fully pumped, indirect system is required, similar to that shown below, noting that the diameter of the flow and return pipes should be 22mm, up to the point in the system where the heating and hot water circuits split.
• Whatever type of system is used, it must be fully pumped and contain a corrosion inhibitor suitable for the copper heat-exchanger.

Although virtually no heat is generated by the boiler when only the cooker burner is in operation, the Rayburn does incorporates its own pump over-run control. Therefore it is necessary to provide a bypass loop, in circumstances where zone valves are fitted which can completely close both circuits. This bypass could incorporate a heat leak such as a towel rail, but otherwise should provide a pipe-work loop of at least 5m from the Rayburn, sufficient to discharge the latent heat. An automatic pressure adjusting valve should be fitted to the bypass.

Since these models incorporate a manual reset overheat device, it is possible to use a sealed system as an alternative to the conventional open-vented arrangement. Sealed systems, set to operate at a maximum pressure of 2 bar, will require the appropriate ancillary equipment, such as expansion vessel, pressure relief valve and filling loop.

Time control for the heating system can be obtained by the use of an external programmer. If this is of the 3 channel type, separate control can be achieved for each of the cooking, hot-water and heating functions. Motorised valves should be used to provide the necessary control, in conjunction with cylinder and room thermostats and may be of the 2 port zone type or 3 port mid-position variety.

If under-floor heating is to be used, this should be a proprietary packaged system, consisting of all the necessary controls etc. Such systems normally require the water temperature through the plastic pipe coils to be restricted to a relatively low temperature such as 30-50 degrees C., but the Rayburn's boiler thermostat must not be used for this purpose, otherwise the domestic hot water temperature would be insufficient and damage to the heat exchanger may result from condensation. Instead, the under-floor equipment manufacturer will normally supply the necessary thermostats and mixing/blending valves to control the water temperature to the heating coils. Always refer to the manufacturers technical literature and instructions.

Thermal store type hot-water cylinders may also be used with these models, in which the heat for the radiators is drawn from the cylinder. Note that two circulating pumps will normally be required. A typical system is shown below, courtesy of Albion Cylinders Ltd and featuring their 'Mainsflow' system.

The system must be installed in accordance with local water bylaws, Building Regulations and standards and we strongly encourage that the plumbing and electrics be carried out by a competent person.