====== Plumbing Definitions ======

Please note these are not definitive definitions they are meant to give some guidance.

|[[plumbing:automatic air vent|AUTOMATIC AIR VENT (AAV)]] | automatically vents air from system whilst filling |[[http://europe.hbc.honeywell.com/products/ecatdata/pg_ea122.html|url]]|
|[[plumbing:air admittance valve|AIR ADMITTANCE VALVE (AAV)]] | allows air to pass in only one direction - __into__ the soil and drainage system |
|AIR SEPARATOR | connects beetween the flow and vent on open system to assist in air removal | [[http://www.screwfix.com/sfd/i/cat/62/p2266862_l.jpg|pic]]|
|AIR VENT | lets air into a room or compartment for combustion or cooling |
|AUTO BY PASS | valve which opens the bypass automatically to suit system demand | [[http://content.honeywell.com/uk/homes/Catalogue/Non%20Electric/5.1%20DU145.pdf|pdf]]|
|BALANCED FLUE | natural draught room sealed appliance | [[plumbing:flues#balanced_flues|wiki]]|
|BOILER | an appliance used to heat water (also see cylinder) |
|BLEEDING | process of removing air from the system by opening bleed points on radiators and pipework |
|BYPASS | pipe linking the flow and return of a boiler used as a means of dissapating exess heat(also see auto bypass) |
|CHANGEOVER / DIVERTER VALVE | used to change the flow of water within a combination boiler between heating and hot water |
|COMBI BOILER | combination boiler where both the heating and hot water are produced in the same appliance |
|COMBUSTION | burning of a fuel |
|CHECK VALVE | non return valve ie only allows flow in one direction | [[http://www.screwfix.com/sfd/i/cat/65/p1850665_l.jpg|pic]]|
|COLD FEED | pipe connecting the feed and expansion tank to the system |
|CYLINDER | tank for producing / storing hot water | [[http://www.screwfix.com/sfd/i/cat/65/p1053465_l.jpg|pic]]|
|IMMERSION HEATER | electric heater for hot water fitted in a cylinder |
|DRAIN TAP | tap with square head and spout to fit hose to (usually on lowest point in system) | [[http://www.screwfix.com/sfd/i/cat/22/p2026322_l.jpg|pic]]|
|EXPANSION / VENT PIPE | used to assist in venting and allowing expansion in a open system (1 size larger than feed) |
|EXPANSION VESSEL | used on a sealed system to absorb the expansion of the heated water |
|FAN FLUE | flue fitted with a fan to assist in the removal of products of combustion | [[plumbing:flues#fanned_flues | wiki]]|
|FILL LOOP | used to fill a sealed system (usually a silver braided pipe with a valve at each end ) | [[http://www.screwfix.com/sfd/i/cat/60/p1939960_l.jpg|pic]]|
|FLOW | passage of heated water away from the boiler |
|FULLY PUMPED SYSTEM | system where the hot water feed and the heating are pumped if it uses two zone valves it is usually refered to as S plan if i uses a diverter valve Y plan (see also motorised valve) | [[http://content.honeywell.com/uk/homes/systems.htm#CPlan] diagrams |url]]|
|GRAVITY SYSTEM | system where the hot water feed is moved by convection and the heating is pumped (usually) |
|HEAT EXCHANGER | primary heats the water directly from the fuel being burned, secondary or domestic used to heat the hot water supply in a combination boiler usually water to water |
|HIGH LIMIT STAT | also known as overheat stat switches the boiler off if the system gets too hot |
|INTERLOCK | Feature(s) of a heating system which prevents boiler from firing when there is no call for heat.  (see Heating Controls for description)|
|MOTORISED VALVE | Valve driven by a motor, 2 port usually called a zone valve | [[http://www.screwfix.com/sfd/i/cat/25/p1085525_l.jpg |pic]]|
|MOTORISED VALVE | Valve driven by a motor, 3 port usually called a diverter | [[http://www.screwfix.com/sfd/i/cat/21/p1758621_l.jpg |pic]]|
|OPEN VENTED SYSTEM | system that is vented to atmosphere (usually to a feed and expansion tank) |
|OPEN OR CONVENTIONAL FLUE | appliance that draws its combustion air from the room in which it is fitted | [[plumbing:flues#open_conventional_flues|wiki]]|
|PUMP / CIRCULATOR | device for circulating heated water round the system | [[http://www.screwfix.com/sfd/i/cat/20/p1723120_l.jpg |pic]]|
|PUMP OVERRUN | extra thermostat to keep the pump running after the boiler shuts down to dissipate heat |
|PROGRAMMER | timer to turn boiler on and off | [[http://www.screwfix.com/sfd/i/cat/11/p2555011_l.jpg|pic]]|
|PROGRAMMABLE THERMOSTAT | thermostat and programmer built into one unit |
|PRESSURE RELIEF VALVE / PRV | spring loaded valve to release exess pressure usually set at 3 bar |[[http://content.honeywell.com/uk/homes/Catalogue/unvented/6.4%20SM192.pdf|pdf]]|
|RETURN | water returning to the boiler to be reheated |
|ROOM SEALED | appliance that takes its air supply from outside the space it is fitted |
|SEALED SYSTEM | system sealed from atmosphere (no tanks) |
|SYSTEM BOILER | boiler with the pump expansion vessel etc built into the case |
|THERMOSTAT | device for controlling temperature (room)| [[http://www.screwfix.com/sfd/i/cat/41/p2903141_l.jpg|pic]]|
|THERMOSTAT | device for controlling temperature (cylinder)| [[http://www.screwfix.com/sfd/i/cat/40/p1056140_l.jpg|pic]]|
|TRV | [[plumbing:thermostatic_radiator_valves_-_trvs|thermostatic radiator valve]] | [[http://www.screwfix.com/sfd/i/cat/96/p2632396_l.jpg |pic]]|
|VENTILATION | vent supplying combustion air |
|ZONE VALVE | see motorised valve | 

[b]AUTOMATIC AIR VENT (AAV) [/b]
automatically vents air from system whilst filling 
pic1(as previous)  or pic2:[img]http://www.bes.ltd.uk/products/graphics/7703.gif[/img](don't know how to put the word in)

AAV's have to have their caps left unscrewed for them to be able to let air out. 
They are used at high points in pipework where air could collect. Sometimes, for example in or near boilers, they MUST be left permanently open.
When they get old they are inclined to scale up and leak water out, in which case they should be replaced.
Note that when the cap is left undone they will let air in if the water is drained from the connected pipe, which can be useful for draining a system.

ChrisR
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[b]AIR ADMITTANCE VALVE[/b]
These are NOT normally referred to as AAV's

Big ones (which fit 100mm diameter pipe or above) are often known by the trade-name Durgo.
They are designed to let air IN to waste or drain system, so that siphoning does not occur. Such siphoning can "pull" the water out of a trap so smelly air passes upwards. They do NOT let air out.
Individual fittings are available from 32mm diameter up, or they can be built in to a trap, such as this one - the little part which looks tacked on the top is the Air Admittance Valve. The traps are known as Vented or Anti-Siphon traps.
[img]http://www.bes.ltd.uk/products/graphics/15521.gif[/img]

ChrisR