Plumbing & heating glossary
Knowing the difference between an immersion thermostat and an immersion element, or a vented and unvented cylinder, makes describing the job and checking a quote much simpler.
Plain-English definitions of 15 plumbing, hot water and central heating terms used by plumbers in Ireland.
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15 plumbing terms explained
- Mains stopcock
- The main shut-off valve on the cold water supply entering the house, usually under the kitchen sink. Turn it clockwise to stop water during a leak.
- Gate valve / lever valve
- Shut-off valves on pipes feeding the hot water cylinder from the attic tank. Older brass gate valves can stick; quarter-turn lever valves shut off cleanly.
- Dual immersion heater
- An electric heating element fitted into the top of a hot water cylinder with two settings: Sink (heats the top of the cylinder) and Bath (heats the whole cylinder).
- Immersion thermostat
- The temperature probe inside the immersion head that switches power off once water reaches around 60 degrees C. Often the part that fails when an immersion stops heating.
- Unvented vs vented cylinder
- A vented copper cylinder is fed from an attic cold tank at low pressure; an unvented stainless-steel cylinder runs at mains pressure for stronger showers.
- Twin-impeller shower pump
- A booster pump fitted in the hot press to pump both hot and cold water from tank-fed supplies to mixer showers and bathroom taps.
- thermostatic radiator valve (TRV)
- A numbered valve on the side of a radiator that senses room air temperature and opens or closes water flow automatically.
- System balancing
- Adjusting the lockshield valves on every radiator so hot water reaches radiators furthest from the boiler at the same speed as those nearest.
- Magnetic central heating filter
- A canister fitted on the return pipe before the boiler that traps black magnetite sludge before it can block the boiler heat exchanger.
- Power flushing
- Circulating cleaning chemicals through radiators and heating pipes with a high-flow pump to clear settled black sludge and restore heat.
- P-trap / bottle trap
- The U-shaped bend under a sink, basin or shower that holds a plug of water to stop sewer smells coming up the waste pipe.
- Siphon / dual-flush valve
- The flushing mechanism inside a toilet cistern. When its rubber diaphragm perishes, water trickles into the bowl or the handle fails to flush.
- Float valve (ballcock)
- The inlet valve that refills a toilet cistern or attic storage tank and shuts off when the water reaches the set level.
- Expansion vessel
- A pressurised tank on a sealed heating system or unvented cylinder that absorbs water expansion as the system heats up.
- Registered Gas Installer (RGI)
- The statutory register for anyone working on domestic gas boilers and gas pipework in Ireland, overseen by Safe Energy Ireland.
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