Heat pump, air con & ventilation glossary
15 heat pump, refrigeration, air conditioning and MVHR terms explained in plain English.
Free, no obligation. One local company prices it, not five.
- €120 to €290a year to service an air-to-water heat pump
- €140 to €400for a fault call-out with a minor repair
- €80 to €210to service an air con unit
- €12,500SEAI's top heat pump grant for a house
Key HVAC & heat pump terms explained
Air-to-Water Heat Pump (Monobloc vs Split)
A monobloc unit keeps the entire sealed refrigerant circuit inside the outdoor casing and sends heated water indoors through insulated flow and return pipes, whereas a split unit connects the outdoor compressor to an indoor hydrobox via copper refrigerant lines.
Backup Immersion & Booster Heater
The electric resistance element (typically 3 kW) inside the hydrobox or hot water cylinder used for weekly 60C legionella pasteurisation cycles; if stuck on due to a sensor or refrigerant fault, it causes a sudden spike in electricity usage.
Buffer Tank / Low-Loss Header
An insulated 30 to 100 litre thermal decoupling vessel installed on zoned radiator and underfloor systems to guarantee minimum water volume and flow rate across the heat pump during defrost cycles even when room stats close.
Defrost Cycle & Four-Way Reversing Valve
The automatic winter routine where an outdoor heat pump briefly reverses its refrigerant flow for 3 to 8 minutes to melt white frost off the outdoor evaporator fins in damp 0C to 5C Irish weather.
Electronic Expansion Valve (EEV)
A stepper-motor-driven metering valve in the refrigerant circuit that continuously adjusts superheat as outdoor air temperatures rise and fall.
Expansion Vessel & System Filling Loop
The sealed pressurised cushion tank and braided filling valve that hold the heat pump water circuit between 1.0 and 1.5 bar cold; a flat vessel or weeping safety relief valve drops pressure below 0.5 bar and triggers a low-pressure shutdown.
F-Gas Certification
The mandatory European and EPA qualification required by law in Ireland for any technician who leak-tests, recovers, tops up, or repairs the sealed refrigerant circuit on a split heat pump, air conditioning unit, or VRF system.
Flow Switch / Vortex Flow Sensor
An internal sensor inside the heat pump indoor unit or monobloc that measures water circulation in litres per minute (typically requiring 12 to 25 L/min depending on kW output) and locks out the compressor if flow drops too low.
Inverter Compressor & PCB Driver Board
The variable-speed DC compressor and high-voltage inverter printed circuit board in the outdoor unit that modulate output between 25% and 100% to match the exact heat loss of the house.
Magnetic Dirt Separator & Y-Strainer
Inline filters on the primary heating return pipe that trap black magnetite iron oxide and gauze debris; a choked strainer is the number-one cause of flow-rate fault codes on Irish domestic heat pumps.
MVHR (Mechanical Ventilation with Heat Recovery)
A whole-house ducted ventilation unit in airtight homes that extracts moist air from bathrooms and kitchens, passes it across a counterflow heat-exchange core to warm incoming fresh air, and requires regular G4/F7 filter changes and fan servicing.
Nitrogen Pressure Test & Evacuation to 500 Microns
Pressurising repaired copper refrigerant pipework with oxygen-free nitrogen (OFN) to verify leak tightness, followed by deep vacuum pumping with a digital micron gauge to remove all moisture before recharging refrigerant by weight.
Plate Heat Exchanger (Refrigerant-to-Water)
The brazed stainless-steel heat exchanger where hot compressed refrigerant gas transfers thermal energy into the central heating and hot water cylinder circuit.
Three-Port Diverter Valve (Heating / DHW)
The motorised brass valve inside the indoor cylinder unit or airing cupboard that switches heated water from the heat pump between the domestic hot water cylinder coil and the space heating circuits.
Weather Compensation Curve
The controller slope linking outdoor sensor temperature to target radiator or underfloor flow temperature (for example, 35C flow at 7C outside rising to 45C at -3C outside); an overly steep curve causes short-cycling and high electricity bills.
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Heat pump and air con repair guides & price breakdowns
Straight answers to what people ask most: itemised costs, specifications, planning or grants, and what to check before you book.
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Questions we get asked
How much does a heat pump repair cost?
A fault call-out with a minor repair is €140 to €400, parts extra. A longer visit with a service is about €399. A refrigerant leak repair and recharge is €290 to €800. See the cost guide.
How often should a heat pump be serviced?
Once a year. Most manufacturers need a yearly service to keep the warranty. It costs €120 to €290.
Is there a grant for repairing a heat pump?
No. SEAI grants don't pay for servicing or repairs. A replacement heat pump unit that hasn't had an SEAI grant before can get up to €6,500. See the SEAI heat pump grant.
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