How to set a Worcester Bosch thermostat

Which Worcester control have you got?

Worcester Bosch has sold several very different controls, and their buttons do not match. Worcester describes the Comfort II RF as a twin channel RF programmable room thermostat paired with a receiver, so heating and hot water run on separate channels. The Comfort+ II RF is the later version, using a Key that plugs into the boiler instead. If your control has no clock, it only holds a temperature, and your times live on a separate timer.

Where the times are set

Setting the temperature right now

On the Comfort range this takes one movement. Turn the selector clockwise to raise the temperature you want, or anticlockwise to lower it. The selected temperature flashes for three seconds, then the new temperature appears briefly with the switching time it applies to.

In Auto mode a temperature you dial in by hand is not permanent: it holds until the next programmed switching time, then the programme takes over. For one that stays put, use the heating select key to choose On, which Worcester defines as heating permanently on.

The four modes explain most "my heating came on by itself" complaints. On is permanently on, Off is permanently off, Auto runs your programmed switching times, and Adv brings the next switching time forward, with a second press restoring the normal programme.

Off is not the same as killing the power at the wall. In Off mode the Comfort+ II RF displays "Permanently" and 5°C, with the frost protection symbol showing, and the heat source supplies heat as soon as the room falls below 5°C to protect against freezing.

Setting the heating times and temperatures

Both models allow up to six switching times a day, each with its own target temperature. You are not setting on and off times. You are setting the moments the temperature changes.

1. Open the main menu. On the Comfort II RF, hold the menu button for more than three seconds. On the Comfort+ II RF, press the menu key until it appears, showing symbols for Heating, DHW (hot water), Holiday, Information and Settings.

2. Turn the selector until a frame surrounds the Heating symbol and press. Time program is displayed. Press again.

3. Choose the days. Mo-Fr shows first. Turn the selector to pick Mo-Fr, Sat-Sun or a single day, then press.

4. Set Time setting 1. The hours flash. Turn to set the hour, press, then repeat for the minutes. This is the first temperature change of the day.

5. Set Temp. setting 1. The temperature indicator flashes. Turn to the temperature you want from that moment on, then press.

6. Repeat for the rest. Worcester's worked example: setting 1 is before getting up, setting 2 after leaving the house, setting 3 before returning home, setting 4 after going to sleep.

7. Stop early if four changes is enough. Where a switching time is not used, press the selector repeatedly after the last temperature without setting anything.

To kill a switching time you already programmed, press until the switching time shows with the hours flashing, turn the hours to 00 and press, then turn the selector clockwise to 00 on the minutes until the display changes to dashes. Hot water works the same way, using DHW 1 on, DHW 1 off and so on.

The numbers worth knowing

All from Worcester Bosch's own published instructions.

• Factory heating programme: 20°C from 06:30, 16°C from 08:30, 21°C from 16:30, 10°C from 22:30. Hot water on at 06:30, off at 08:30, on at 16:30, off at 22:30.
• The UK Health Security Agency advises people to "try to heat rooms you spend a lot of time in, such as the living room or bedroom, to at least 18°C".
• Signal strength shows as 0 to 10 in the Info menu. The Comfort+ II RF manual reads 0 as no reception, 1 to 3 poor, 4 to 6 good and 7 to 10 very good. The Comfort II RF manual words the same bands as no signal, weak, acceptable and very good.
• Batteries are LR6/AA 1.5V alkaline. Once the weak battery symbol shows, Worcester says replace them within 60 days or the programmed settings are lost.
• Reset all restores the factory settings, and everything you set has to be re-entered.

Two settings people miss: Holiday and the key lock

Holiday mode is the tidy way to leave for a fortnight. Select the Holiday symbol, press the selector, change Off to On, then set the day and month of the start and end dates. The programme becomes active at midnight on the first day set and inactive at midnight on the last. Heating and hot water switch off while it runs, with frost protection still watching below 5°C.

The key lock stops small hands rewriting your programme. On the Comfort+ II RF, hold the heating select key and the selector together until Key lock is displayed, and repeat to switch it off. On the Comfort II RF it is the CH select button and the knob, held for more than three seconds.

Where the thermostat sits changes everything

A thermostat reading the wrong temperature will never hold a room properly, however carefully you programme it. Worcester's instructions for the Comfort II RF are specific: free air flow, an open area, not obscured by curtains or furniture, no closer than 300mm to metal objects including metal wall boxes, on a wall not subject to direct sunlight or draughts, preferably an inside wall 1.2 metres above the floor, and never directly influenced by radiators, televisions or lamps.

Because these controls modulate the boiler, Worcester says the required room temperature must only be set once at the control unit, and that the radiator valves in the room holding the thermostat should be opened completely. If the TRV beside your thermostat is turned down, the two controls fight each other.

If no flame symbol appears, the temperature may simply be close to the target, and the control has turned the boiler off early to prevent overshoot. Worcester's fix is to set the target at least 2°C above the displayed temperature, then allow up to 6 minutes for the flame.

Set correctly and the heating still will not run

At that point the problem has usually moved from the settings to the hardware.

Loss of RF signal shows as fault code A21 or A22 on the Comfort II RF. Worcester's causes are the thermostat being incorrectly positioned, or the receiver or thermostat having no power, including flat batteries. A21 also appears at initial switch on until the units establish a link, so allow up to a minute after power up. When the signal is lost the receiver's LED flashes once a second, which Worcester calls a local error rather than a boiler fault, and its override push button can be pressed once for less than three seconds to switch the boiler on or off by hand. Do not hold it, because holding it for more than five seconds starts pairing and more than ten seconds unpairs the receiver, which would leave you with no heating control at all.

If the room never reaches the temperature you set, Worcester lists an airlock, low system pressure, the programme not running long enough, a low flow temperature, and a sticking radiator valve in the reference room.

The Comfort II Room thermostat also displays boiler fault codes, so the code you see may belong to the boiler. Our list of <a href="/blog/worcester-bosch-boiler-fault-codes/">Worcester Bosch fault codes</a> covers the common ones, and our page on a <a href="/manufacturers/worcester-bosch/help/thermostats/">Worcester Bosch thermostat not working</a> goes deeper.

One safety point sits above all this. Your thermostat is a low-voltage control, but the appliance it operates burns gas. Never open the boiler casing and never work on the gas supply. If you smell gas, do not touch electrical switches, do not smoke, put out naked flames, open the doors and windows, and contact the National Gas Emergency Service immediately on 0800 111 999.

Getting a heating engineer out

If the settings are right and the heating still will not fire, book a repair and we will arrange a Gas Safe registered engineer to attend and diagnose it. We work with a national network of thousands of Gas Safe registered engineers, so call us on 0333 772 6247 or ask for a callback. To spread the cost of future breakdowns instead, look at our <a href="/cover/boiler-central-heating/">boiler and central heating cover</a>.

Worcester Bosch thermostat FAQs

Settings right and the heating still will not run? Book a repair.

Book a repair and we will arrange a Gas Safe registered engineer to attend and diagnose it. One-off repair visits run Monday to Friday, 09:00 to 17:00. A £95 call-out fee applies and is paid in advance, and the engineer tells you what is needed and what it costs before any work goes ahead. One-off repairs do not carry a workmanship guarantee. Smart Plan cover is a separate product for future breakdowns, so a fault showing today counts as pre-existing and is not covered. For the faults it does cover, the boiler and central heating module pays parts and labour up to £500 in a 12-month period if your boiler is under 7 years old, or up to £200 if it is over 7. On a cover plan we aim to get an engineer out to you within two working days, and cover-plan call-outs run Monday to Friday, 08:00 to 18:00. On a cover plan a £95 call-out fee, paid in advance, applies in your first 30 days, for faults the plan does not cover, no-access visits and early annual-service requests. Cover still applies during those 30 days. Using a module starts a 12-month agreement period once you first use a service; there is a 14-day cooling-off period, which ends the moment a service is carried out, and leaving early after that costs the remaining months or 75% of the outstanding balance. It is a service plan, not insurance.

Helpful links

• Worcester Bosch thermostat not working
• Worcester Bosch boiler fault codes
• No heating? Book a repair
• Boiler & central heating cover
• Worcester Bosch boiler control manuals
• Check an engineer on the Gas Safe Register
• UKHSA: keeping warm and well in cold weather