Radiator TRVs and Heat Pumps: How to Set Them

If you have just had a heat pump installed, you might be confused about your thermostatic radiator valves (TRVs). The settings that worked with your gas boiler will not work the same way with a heat pump. Set them too low and rooms will not warm up. Set them too high and you lose the ability to control individual rooms. And the relationship between TRVs and weather compensation — which most heat pumps use — is something many homeowners (and some installers) get wrong.

This guide explains how to set your TRVs correctly for a heat pump system, why the approach is different from gas, and how to get the best balance of comfort and efficiency.

How TRVs Work

A thermostatic radiator valve is a self-regulating valve fitted to a radiator. It contains a temperature-sensing element (usually a wax capsule or liquid-filled bellows) that expands or contracts with the room temperature. When the room reaches the set temperature, the valve closes and stops water flowing through the radiator. When the room cools, the valve opens to allow warm water in again.

TRVs are numbered, typically from 0 (off) to 5, with each number corresponding roughly to a temperature:

These temperatures are approximate and vary between manufacturers. They assume the TRV sensor is in free air near the radiator — obstructions, curtains, or radiator covers can affect the reading.

Why TRV Settings Are Different with a Heat Pump

Lower Water Temperature Means Less "Headroom"

With a gas boiler, the water reaching the TRV is 60 to 75°C. There is an enormous temperature difference between the water and the room, so the radiator can deliver heat aggressively. Setting a TRV to 2 or 3 works because the radiator has plenty of spare capacity — it can heat the room rapidly and then the TRV closes.

With a heat pump, the water temperature is only 35 to 50°C. The radiator is already working closer to its limits. If you set the TRV low (1 or 2), the valve starts closing before the room is properly warm, restricting flow to a radiator that is already delivering modest heat. The result: the room never reaches a comfortable temperature.

The General Rule: Set TRVs Higher Than You Did with Gas

With a gas boiler, you might have set living room TRVs to 3 and bedroom TRVs to 2. With a heat pump, you typically need to set them one to two notches higher:

• Living rooms and kitchens: 4 (or fully open/maximum)
• Bedrooms: 3 to 4
• Bathrooms: 4 to 5
• Hallways and landing: 3
• Spare rooms (less used): 2 to 3

Many heat pump installers actually recommend leaving TRVs fully open (setting 5 or removed entirely) on the main living spaces and letting the heat pump's weather compensation control the overall temperature. More on this below.

TRVs and Weather Compensation: Working Together

Most modern heat pumps use weather compensation — an outdoor temperature sensor that automatically adjusts the flow temperature based on how cold it is outside. This is the primary temperature control mechanism in a heat pump system, and it changes the role of TRVs significantly.

With a Gas Boiler

The boiler fires at full temperature regardless of the weather. TRVs are the main way rooms are individually controlled — they open and close frequently to maintain the set temperature.

With a Heat Pump

Weather compensation adjusts the flow temperature so the radiators deliver roughly the right amount of heat for the conditions. On a mild day, the flow might be 32°C — just enough to maintain room temperature without the TRVs needing to close at all. On a cold day, the flow rises to 45°C to deliver more heat.

In this setup, the TRVs serve mainly as safety valves — preventing individual rooms from overheating rather than being the primary temperature control. This is why many installers recommend setting TRVs to 4 or 5 and letting weather compensation do the heavy lifting.

Why This Matters for Efficiency

If TRVs close too frequently (because they are set too low), they restrict water flow through the system. This can cause several problems:

• Short-cycling: With multiple TRVs closed, the heat pump has nowhere to send its heat. It cycles on and off rapidly, which wastes energy and increases wear on the compressor.
• Reduced efficiency: Short-cycling prevents the heat pump from running at its optimal steady state, reducing COP.
• Uneven heating: Rooms with open TRVs receive excess heat while rooms with closed TRVs get none.

A buffer tank or low-loss header can mitigate short-cycling, but the best approach is to set TRVs appropriately and let weather compensation manage the overall system temperature.

Recommended TRV Strategy for Heat Pump Systems

Option 1: TRVs Wide Open, Weather Compensation Controls Everything

This is the simplest approach and works well in homes where all rooms have similar heating needs. Set all TRVs to 5 (or remove them) and rely entirely on weather compensation to regulate temperature. The heat pump sends water at exactly the right temperature for the conditions, and every radiator receives the same flow.

Pros: Maximum efficiency, no short-cycling, even temperatures throughout the house.

Cons: No individual room control. Rooms with different orientations (south-facing vs north-facing) or internal heat gains (kitchen vs bedroom) may be at slightly different temperatures.

Option 2: TRVs Set High with Selective Adjustment

Set most TRVs to 4 or 5, and use lower settings only in rooms where you specifically want a cooler temperature (spare bedrooms, home offices when unoccupied). This provides some room-by-room control without restricting the system too aggressively.

Pros: Good balance of efficiency and comfort. Prevents overheating in south-facing or internally heated rooms.

Cons: TRVs in lower settings may cause minor flow restriction.

Option 3: Smart TRVs with Heat Pump Integration

Smart TRVs (such as those from Tado, Drayton Wiser, or Honeywell Evohome) replace mechanical TRVs with electronically controlled valves connected to a smart thermostat. These systems can communicate with the heat pump to:

• Control each room to a precise temperature set by the user
• Adjust the heat pump's flow temperature based on which rooms need heat
• Ensure enough zones remain open to prevent short-cycling
• Learn your schedule and pre-heat rooms before you need them

Smart TRVs are the most sophisticated option and offer the best individual room control. However, they are more expensive (£40 to £80 per valve plus the smart thermostat hub at £150 to £250) and require setup and configuration.

Cost for a whole house: £400 to £800 for a typical three-bedroom home.

Common TRV Mistakes with Heat Pumps

Setting All TRVs to 2-3 (Like You Did with the Boiler)

This is the most common mistake. At heat pump flow temperatures, setting 2 or 3 means the TRV begins closing before the room has properly warmed. The room stays cold, and the homeowner blames the heat pump when the real issue is the TRV setting.

Closing TRVs in Unused Rooms Completely

Turning TRVs to 0 in multiple rooms simultaneously reduces the number of open radiators, potentially causing the heat pump to short-cycle. It is better to set unused rooms to the frost protection setting (*) or setting 1, which keeps some flow but reduces heat to a minimum.

Covering TRVs with Curtains or Furniture

A TRV blocked by a curtain or piece of furniture reads a higher temperature than the actual room temperature (because trapped air around the radiator is warmer). It closes prematurely, and the room stays cold. Ensure TRV sensors are exposed to room air. If the radiator is behind a curtain, consider a TRV with a remote sensor that can be positioned in the open room.

Not Replacing Stuck or Faulty TRVs

Old TRV heads can seize up, leaving the valve permanently open or permanently closed. Before or during a heat pump installation, check that all TRVs operate freely. Replace any that are stuck — a new TRV head costs £10 to £30 and can be swapped in minutes.

Zoning: An Alternative to TRVs

Some heat pump installations use zone valves instead of (or alongside) TRVs. Zone valves are motorised valves fitted to pipework that divide the house into two or more heating zones — for example, downstairs and upstairs, or day zones and night zones.

With zone valves, you can:

• Heat the living areas during the day and reduce upstairs heating
• Heat bedrooms in the evening and overnight while reducing living area heating
• Run underfloor heating at a different temperature to radiators

Zone valves must be designed so that at least one zone is always open, preventing short-cycling. Many systems include a bypass valve or buffer tank as a safety measure.

Balancing TRVs and Lockshield Valves

Each radiator has two valves: the TRV on one side and a lockshield valve on the other. The lockshield valve controls the flow rate through the radiator and is set during commissioning using a small spanner.

For heat pump systems, correct lockshield balancing is important. The installer should adjust each lockshield valve so that:

• The flow rate through each radiator is appropriate for its size and output
• The temperature drop across each radiator (flow minus return) is consistent — typically 5 to 7°C for heat pump systems
• No single radiator receives a disproportionate share of the flow

Poor balancing can result in some radiators being warm while others stay cold, regardless of TRV settings. If your system seems unevenly heated, ask your installer to check the balancing.

Frequently Asked Questions

What should I set my TRVs to with a heat pump?

Set living rooms and kitchens to 4 or 5, bedrooms to 3 or 4, and bathrooms to 4 or 5. This is higher than typical gas boiler settings because the heat pump operates at lower water temperatures. In many cases, setting all TRVs to maximum and relying on weather compensation is the most efficient approach.

Should I turn TRVs off in rooms I do not use?

Avoid turning multiple TRVs to 0 simultaneously, as this can cause the heat pump to short-cycle. Set unused rooms to the frost protection (*) or 1 setting instead. This maintains a minimal flow and prevents the rooms from getting so cold that they drain heat from adjacent rooms.

Do I still need TRVs if I have weather compensation?

TRVs are not strictly essential if you have weather compensation, but they are useful for fine-tuning individual rooms. They prevent rooms with south-facing windows or internal heat sources (kitchens, rooms with computers) from overheating while other rooms need full heat output.

Are smart TRVs worth the money with a heat pump?

Smart TRVs offer the best individual room control and can improve comfort and efficiency. They are particularly useful in homes where different rooms are used at different times. The cost (£400 to £800 for a whole house) can be offset by efficiency gains over a few years. However, a well-set-up system with standard TRVs and good weather compensation can perform nearly as well at lower cost.

Why is my radiator cold at the bottom?

A radiator cold at the bottom usually indicates sludge buildup, not a TRV problem. This is a common issue in older systems and should be resolved with a powerflush before or during the heat pump installation. A cold patch at the top suggests air in the radiator — bleed it using the bleed valve.

Can I remove TRVs entirely?

You can replace the TRV head with a manual handwheel valve, which stays fully open. This is sometimes done on radiators in key rooms where you never want the flow restricted. Keep TRVs on rooms where some degree of individual control is useful.