Thermostat and TRV Settings for a Warmer, Cheaper Winter

A room thermostat turned up to 23C, every radiator valve wound to 5 and a programmer still on its factory times is a very common set-up. It usually means some rooms are too hot, others never warm up, and the boiler burns more gas than it needs to. Late August is a good time to sort the settings out, before you are relying on them every day.

What temperature should your room thermostat be set to?

For most homes a room thermostat set between 18C and 21C is right. Start at 19C or 20C, live with it for a few days, then move it one degree at a time until the house feels comfortable. Every degree you can knock off without feeling cold reduces the gas your boiler burns.

The thermostat is a switch, not a volume knob. It tells the boiler to fire until the room it sits in reaches the set temperature, then to stop. Turning it to 28C when you come in cold does not warm the house any quicker. It just means the heating runs on long after you are comfortable.

Position matters too. A thermostat in a draughty hall, next to the front door or in direct sunlight will give a false reading. If yours is badly placed, a wireless thermostat that can sit in the main living room is a simple fix, and it is something to raise at your next service.

What do the numbers on a TRV mean?

The numbers on a thermostatic radiator valve (TRV) roughly correspond to room temperatures. On many common valves, 3 is close to 20C and each number up or down is worth around 3 to 4 degrees. The exact figures vary by manufacturer, so treat the table below as a guide and check the maker's leaflet if you have it.

A TRV senses the air around its head and closes as the room reaches its setting. That means a TRV hidden behind a long curtain or a sofa will shut off early, because it is reading a pocket of warm air rather than the room.

Should there be a TRV in the room with the thermostat?

No. The room with the main thermostat should have a radiator without a TRV, or with its TRV left fully open. If the TRV closes first, that room never reaches the thermostat's setting, so the thermostat keeps calling for heat and the boiler keeps firing while the rest of the house overheats.

This is why new boiler installations normally leave that one radiator on a plain valve. If you have a TRV in your thermostat room, simply turn it to its highest setting and let the thermostat do the controlling.

How should you set TRVs room by room?

Set each room for how you use it, not all to the same number. A sensible winter starting point for a typical Stoke-on-Trent terrace or semi looks like this:

• Living room: 3, or fully open if the thermostat is in there.
• Bedrooms: 2 to 3, depending on whether you like a cool room for sleeping.
• Bathroom: 3 to 4, since it is used briefly and needs to dry out.
• Hall and landing: 2, unless the thermostat is there.
• Spare rooms: 1 or 2 with the door shut. Avoid switching them off completely in a cold spell, as unheated rooms against outside walls are prone to condensation and mould.

Give each change a day before judging it. TRVs are slow by design.

How should you set the programmer for winter?

Most homes do well with two heating periods on weekdays: one starting 30 to 60 minutes before you get up, and one starting before you come home. Switch the heating off around half an hour before bed, because the house holds its warmth for a while.

Weekends often need a different pattern, so use the separate day settings if your programmer has them. If you have a hot water cylinder, time the hot water to finish heating just before you need it rather than running all day.

The Energy Saving Trust recommends using a programmer, room thermostat and TRVs together, and that is the combination that gives you real control. Your boiler's flow temperature is the other half of the picture; see what your boiler flow temperature should be.

Why is one radiator still cold with its TRV on 5?

If a radiator stays cold at the top, bleed it first; our guide on how to bleed a radiator covers the steps, and remember to check the boiler pressure afterwards. If it is warm at the top but cold at the bottom, that points to sludge rather than air.

If working the TRV has not freed it and bleeding makes no difference, the valve pin is probably seized or the system needs balancing. Both are straightforward jobs for an engineer and can be looked at alongside a service.

Getting your controls checked in Stoke-on-Trent

An annual boiler service in Stoke-on-Trent is a good moment to ask the engineer to look at your thermostat position, programmer settings and any sticking valves. If you are thinking about better controls or rebalancing, our central heating team can advise on what is worth doing. We also cover boiler servicing in Newcastle-under-Lyme. Call us on 07896 677083, seven days a week between 9am and 5pm.