2 Central Heating Systems: Open Vented System

• The lesson aims to help learners identify central heating components.
• The purpose of a central heating pump, and its best location, will be examined.
• The internal mechanisms of a Feed & Expansion Cistern will be understood.
• Learners will understand the importance of balancing a central heating system and how to achieve it.

Open Vented System

• A feed and expansion cistern is used in open vented systems.
• It fills the system with water.
• Cisterns are located in the loft, at the system's highest point.
• F&E cistern bases should align with the cold water storage cistern and be fully supported.
• The main function of the F&E is to facilitate heated water expansion at atmospheric pressure.
• F&E cisterns are typically 18-litre, black plastic containers.
• A 15mm cold feed connects to the F&E side and must be free of valves.
• A 22mm open vent from the primaries is located above the F&E, rising at least 450mm above the water level without valves.
• F&E cisterns should be positioned at least 1 meter above the circulator.

Float Operated Valve (FOV)

• The rising main feeds the BS 1212 FOV in the F&E, preceded by a service valve for maintenance.
• The water level set by the FOV should barely cover the cold feed exit to allow for expansion.
• Heated system water expands by 4%, accommodated in the F&E.

Open Vent Pipe

• The main role of the open vent pipe is to serve as a safety outlet if the system overheats.
• This pipe allows the system to function at atmospheric pressure.
• The open vent enables air to escape while the system fills and operates.
• It must be free of valves to prevent potential blockage of the cold feed.
• The vent needs to be at least 450mm above the water level to prevent pump surge.
• The minimum pipe size is 22mm.

Air Separator

• An air separator enables close proximity or close-coupled pipework for the cold feed and vent pipes.
• The air separator is an oversized pipe with cold feed and vent pipe connections.
• It separates air by swirling water.
• Correct pipework and air removal reduce noise and the risk of corrosion in the system.

H Frame Configuration

• As an alternative to an air separator, an H frame configuration is commonly used.
• The vent and cold feed need to be installed on the flow from the boiler.
• Install it on the suction side of the circulator, with a maximum of 150mm between them
• Ensuring the circulator always draws on the cold feed.
• Correct pipework ensures the system's neutral point is at the cold feed base.

Circulator

• Pump positioning is crucial for positive pressure and to avoid air entering the system, preventing corrosion.
• The circulator must always draw on the cold feed.
• Circulators have speed settings to efficiently heat the system without noise.
• A circulator uses pump flanges to maintain a watertight seal via rubber or fibre washers.
• Full bore valves allow removal without draining the system.
• If radiators aren't heating and hot water is lukewarm, the pump may need replacing.
• Isolation valves are integral to the flanges for easy maintenance.
• The position of the circulator, relative to the cold feed and vent pipe, is important for positive pressure.

Two Port Motorised Valve

• Zone valves are activated by a room or cylinder thermostat.
• They enable separate control of hot water and heating circuits.
• The zone valve opens to allow water from the boiler to circulate. When the thermostat is up to temperature, the zone valve closes to isolate.

Three Port Mid-Position Valve

• These valves control water flow to both heating and hot water circuits, reacting to cylinder and room thermostats.
• Ports are labeled AB (flow from boiler), A (central heating), and B (hot water).
• In mid-position, the valve allows water to circulate around both heating A and hot water B circuits.
• In heating mode only, water is allowed to circulate around the central heating circuit (port A).
• In central heating mode only, water is allowed to circulate around the hot water circuit (port B).
• Water can always flow through this valve.

Cylinder Thermostat

• Cylinder thermostats are located one-third of the way up a hot water cylinder.
• The thermostat governs the hot water temperature.
• It's linked to the zone valve or three-port valve.
• These thermostats can be bi-metallic strip, volatile liquid, or gas type.
• They are commonly set to a maximum of 60°C.

Room Thermostat

• Room thermostats are located 1.5 meters up a wall and approximately 3 meters from a heat source, avoiding outside walls.
• They can be basic bi-metallic or programmable Wi-Fi/app-activated digital types.
• Compensating room thermostats are also common.

Boiler Thermostat

• Boiler thermostats are located on the boiler.
• They govern the temperature of the primary water.
• The water heats the heat exchanger in the hot water cylinder, as well as heating the heat emitters in each room.
• Boiler thermostats include a phial on the boiler's return pipe, indicating when the system is up to temperature.

Programmer

• Programmers allow independent, timed control of hot water and central heating.
• They are commonly situated in the kitchen or airing cupboard.
• These often include a boost or override button to operate outside programmed timings.

Frost Thermostat and Pipe Thermostat

• These thermostats prevent vulnerable parts of the system from freezing.
• They override the programmer and other thermostats, set between 3ºC and 5°C.
• Frost thermostats are positioned in vulnerable areas, and pipe thermostats.
• They activate the circulator and boiler briefly to warm the system water.

Working Safely

• When working on any electrical components, including the boiler, safe isolation procedure is vital to ensure no one accidentally turns on the system.
• This involves switching off the fused spur, removing the fuse, locking off the fuse holder, and putting up a sign indicating work is in progress.
• When working on a domestic system it needs to be communicated to the customer and other people in the property.
• Communication needs to cover how long it will be out of service for and also when decommissioning a system.

Magnetic System Cleaner

• Magnetic system cleaners, of various styles and makes, contain a magnet to collect corroded iron particles (magnetite).
• During system service, the magnet is removed to flush away the magnetite, keeping the system water in good condition.

Inhibitor

• Inhibitors chemically protect against scale and corrosion in central heating systems.
• They can be added via the F&E tank or a radiator.
• Inhibitor levels can be tested and topped up.
• Inhibitors are claimed to extend system life, maximizing efficiency and minimizing fuel usage.
• The primary vent must terminate over the F&E tank, due to the chemical content.

Radiator Valves

• Radiators fit at either end of a domestic radiator.
• One with a wheel head, which the customer can turn. This alters the flow of water into the radiator to suit the customer's needs.
• A lock shield valve is placed on the opposite end of the radiator.
• A lock shield is identical to wheel head, except it has a wheel removed.
• Lock shield caps are put in its place for the engineer to balance the system.

Balancing the System

• The lock shield valve balances the system during commissioning.
• Unbalanced systems cause non-uniform radiator warming and can affect the 10°C temperature difference between flow and return pipework.
• System water circulation faces resistance from pipework, fittings, and bends.
• Water takes the path of least resistance, so some radiators might heat up quicker and others may stay cool.
• Open wheel head valves fully on all radiators.
• Open all lock shield valves half way.
• Turn on the boiler, selecting both CH & HW.
• Take the temperature of all radiators to see if they are warming uniformly.
• If a radiator's is heating too much/little, adjust suits the lock shield to suit.
• Put the lock shield back on when they have achieved the same temperature.

Radiator Key

• Use PTFE tape, hemp, and paste for the watertight seal on the threads when making up a radiator.
• Valves are screwed into the radiator using a radiator key.
• TBOE = top bottom opposite ends.
• BBOE = bottom bottom opposite ends.
• A bleed key is needed to bleed any air or is from the radiator, it is used on the top of radiators.

Bleed Key

• An air release valve is located at the top of every radiator and towel rail.
• This allows manual release of air.

Thermostatic Radiator Valve

• Thermostatic Radiator Valves requires TRVs to be fitted on systems.
• This valve replaces the wheel head valve.
• It allows the customer to control the temperature of a single radiator
• It has a special head, which reacts to ambient air temperature.
• A sensor inside the head contains a volatile liquid when heated expands.
• The warmer the room's temperature, the closing of the valve of pushing a pin down in the valve.
• The room temperature cools, the liquid contracts, there by opening the valve again and allowing the radiator to heat back up.
• One radiator in the circuit must be left without a TRV fitted.
• Building Regulations state this should be the radiator in the same room as the room stat.
• If a radiator fitted with a TRV is removed for decorating, place a decorators cap over the head to the valve.
• If the customer has long curtains, remote heads should be installed.
• TRVs are mostly placed on the flow but it doesn't matter so be careful when fitting.
• Noise can occur if customer ends up with something noisy.
• These items can be fitted with remote sensors, allowing TRVs to operate despite interference from curtains or furniture.

Automatic Bypass Valve

• ABV is fitted on most Modern systems.
• Allows build up of systems if thermostatic radiator valves close.
• Circulator will continue to operate.
• Relieves through system pipe work which helps prolong pump life.
• ABV its between the primary flow and return pipe.
• Some boilers already have an ABV installed.
• This allows water to flow through the boiler if the TRVs and zone valves close.

Filling Loop

• This is a flexible, temporary connection between the incoming mains and the central heating system.
• It's used on pressurized sealed systems, like combination boilers.
• Water Regulations require it to be disconnected after use.
• There is a quarter-turn isolator on both sides of the loop.
• The incoming mains is protected by a double check valve, as Water Regulations require.

Expansion Vessel

• Used on a sealed system to take up the 4% expansion of the heated water.
• Sized depending on the system.
• A rubber diaphragm/bladder is located inside the vessel.
• On the drier side it is changed through a schrader valve with 1 Bar of pressure.
• Expanded water pushes against the diaphragm on the wet side to compress the air.

Pressure Relief Valve

• When a sealed system over-pressurises a PRV is installed (Pressure Relief Valve).
• Allowing the access pressure to discharge safely.
• Discharge Pressure is factory set.
• A build up of pressure can occur when the expansion vessel fails or loses its charge.

Automatic Air Release Valve

• Found fitted inside boilers as well as high points inside systems.
• Automatic Air Release Valves allow air to be released from systems and close automatically.