• Welcome to PlumbersForums.net - The international free plumbing advice forum. Professional plumbers sharing advice with fellow plumbers and DIY alike. Register for free today! - Checkout the Plumbing Advice forum and then our Plumbing Videos area which still needs populating.


A thermostat is a regulating device component which senses the temperature of a physical system and performs actions so that the system's temperature is maintained near a desired setpoint.
Thermostats are used in any device or system that heats or cools to a setpoint temperature, examples include building heating, central heating, air conditioners, HVAC systems, water heaters, as well as kitchen equipment including ovens and refrigerators and medical and scientific incubators. In scientific literature, these devices are often broadly classified as thermostatically controlled loads (TCLs). Thermostatically controlled loads comprise roughly 50% of the overall electricity demand in the United States.A thermostat operates as a "closed loop" control device, as it seeks to reduce the error between the desired and measured temperatures. Sometimes a thermostat combines both the sensing and control action elements of a controlled system, such as in an automotive thermostat.
The word thermostat is derived from the Greek words θερμός thermos, "hot" and στατός statos, "standing, stationary".

View More On Wikipedia.org
  1. N

    Timer and Thermostat Update

    Hi all, I have a mechanical timer (5 wire not including ground) by the boiler for heating & water and a thermostat in the living room. The timer keeps missing switches so not coming on/off automatically. I could replace it like for like but I'm considering removing it and changing the...
  2. zack6600

    How to replace thermostat cartridge

    Hi Folks, Need your advice on how to access a thermostat cartridge to fix/replace. Please see pics below. I have manged to to get the main shower control cartridge out as it is leaking badly. But now need to sort the thermostat/mixer out now as very stiff and difficult to turn to cold. The...
  3. J

    Boiler doesn’t want to listen to (Hive) Thermostat

    Hi - this is driving me nuts and I can’t figure it out so any thoughts welcome. The hive receiver at the boiler is correctly receiving a signal from the thermostat to turn the heating on - but then… nothing! This definitely isn’t a hive communication issue given (a) the hot water via hives...
  4. M

    Removing thermostatic valve to clean

    I have a thermostatic concealed shower and would like to remove the thermostatic valve and look to clean any debris as it doesn't appear to be getting very hot, other showers are fine. It's around 6 years old. It was installed by a plumber and bought from a company in Wales, have been told it...
  5. R

    Thermowatt thermostat

    I have a thermowatt RTS-3 red immersion. I would like to replace the thermostat which is red can I replace it with a higher temperature thermostat.
  6. L

    How do I fit Bosch thermostatic valves to old radiators .

    background: I have 15 radiators 20+ years old with no thermostatic valves and Bosch instructions depend on replacing the actuator part only of old thermostatic valves. Surely there is an option for new complete valve replacing? Tom
  7. A

    Thermostat ticking very loud. What can I do? Ok

    My thermostat ticks very loud, what can I do?
  8. P

    The HWC Mystery - only reaches 50c despite a tested thermostat...

    Background - One morning about two weeks ago I found we had hot water in the cold water tank, so I ran off the cold (now hot) water and let the cold tank refill to try and diagnose the reason. But the cold tank has stayed cold ever since after that with nothing coming back from the hot cylinder...
  9. T

    URGENT Thermostat not firing up boiler, Salus/Greenstar

    Hi! I'm wondering if anyone can help me get my radiators on :) My Salus ST620WBC ran out of battery after ticking over nicely for years. Got it back on OK .... but now the 'reciever' on the boiler (a Worchester Combi 30si) is not working. It was left with no signal for a day yesterday. I got...
  10. 6

    Testing a Type TSR thermostat

    Hi all, I am looking for some advice to test the correct operation of a TSR thermostat for an immersion water heater. In the past with the old type of thermostats I would test for continuity between the live and neutral (when disconnected). Is this the same procedure for the the Type TSR...
  11. J

    Replacing a Honeywell T40 thermostat with a Honeywell DT90e

    Hi I'm replacing my old dial thermostat with a digital The wires going in from left to right are Earth Blue 2x Black Brown When electrically tested none are live with thermostat off Research on this and other sites suggest 2x Black into B Brown into A Tie off and isolate Green/Yellow and Blue...
  12. G

    Recommended smart thermostat/controller for ATAG combi (ATAG or Tado)

    Hi all I'm considering getting an ATAG IC Economiser (combi), and to take advantage of the 14 year warranty I need to get one of 2 smart controllers: ATAG One Zone Tado v3+ An annoyance about the Tado is that the UK version doesn't support OpenTherm (unlike the EU model), but this is...
  13. S

    Honeywell thermostat replacement

    I need to replace our Honeywell CM721, I believe the modern replacements would be either Honeywell T3R or T4R, is this correct and would the receiver also need replacing or would the T's mate up to my original Honeywell receiver?
  14. Q

    Worcester MT10RF mechanical rf thermostat is broken all cogs fell out

    Hi I have a Worcester MT10RF mechanical rf thermostat and it is broken dropped and all cogs dislodged leaving me confused how they put together. I have sat there for 3 hours straight working it out and still can't get it together even left with a orange peace that I have no clue were it goes...
  15. M

    Smart TRV and room thermostat replacement

    Hi, A bit of background first I have a air source heat pump, downstairs is all underfloor heating and controlled by individual room thermostats. I am happy with this setup and can control this centrally (a heatmiser solution which I may add smarts to later). For hot water I have a simple...
  16. G

    Thermostat broken, boiler heating rads up constantly

    My valiant thermostat has broken (kids knocked off table and wiring inside stat became disconnected) now the boiler is constantly heating up the radiators and house. Any idea how to fix!
  17. C

    Worcester 35 HE plus boiler/ tr2 thermostat controller replacement

    Ive moved into a house with a worcester greenstar 35 HE plus boiler in the garage. The TR2 thermostat controller is hanging loose on the wall in the living room, and is faulty. I want the TR2 replaced with a controller i can set a timer on, either digital or mechanical, the TR2 has three wires...
  18. M

    Replacing old thermostat for Nest

    Hi all, I want to replace my current thermostat with the Nest Thermostat, but wire labels don't match. My boiler is Worcester Greenstar 24i Junior combi boiler, which is on the back of the wall where the thermostat is. Photos here Another Nest Themorstat (3rd gen) question -...
  19. T

    Best direct replacement for old Landis & Staefa Room Thermostat

    We have a very old Landis & Staefa room thermostat which I would like to replace with a simple like for like model. I cant see a model number on this so just have this image. Can someone recommend a suitable replacement please?
  20. S

    Potterton Performa 30 HE and relay switching thermostat (Tado)

    I have now established that my boiler, a Baxi Potterton Performa 30 HE will only work in relay (on/off) mode. Looking at the wiring diagram below, which terminals would I connect to the new version of the extension box? Tado won't tell me. When I installed my first Tado system on an older...