What you do if your boiler isn’t responding to the thermostat

 
You’ve been in the house all day, your heating is on, and when you check it has reached the temperature. Then you go out for a few hours and when you get back it’s not even warm in the hallway. You start to think that maybe your boiler isn’t working - but then why would it heat up if it wasn’t going to stay hot?

There could be several reasons why your rooms are not warm after switching on the heating. It may be that your boiler is not getting power, water is building up inside the boiler or a boiler leak. However, a common reason why your rooms are not warm after switching on the heating is a fault with the thermostat.

Here we discuss why your boiler isn't responding to your thermostat and common questions that come up about thermostats in general.

Why isn't my boiler responding to the thermostat?
There are a few possible reasons why your boiler is not responding to the thermostat:

• The battery in your thermostat has run flat and needs replacing.
• The wiring between the valve and thermostat may need adjusting or checking due to loose connections or damage.
• Your room temperature sensor (radiators) may need adjusting or re-fitting.
• Your heating needs to be in a separate zone from the hot water system.

How do boiler thermostats work?
Your boiler thermostat helps regulate the room temperature by switching on and off your heating system when it is required. It has a few different components that work together.
The main part of the thermostat is the dial face that displays the room temperature. This dial should be set to suit your needs, i.e., if you like a room to be warm, you can set the thermostat so that it switches on when the room temperature meets your requirements. When your heating needs to switch on, a metal bar inside of the dial is pushed away from ‘0’. A different resistance occurs depending on which temperature band this metal bar has been pushed to.
 
In turn, this leads to a current passing through the heating which controls your boiler. The way that this works is using a 24V alternating current, where the voltage switches from positive to negative and back again at a frequency of 50Hz. This current flows through a transformer before reaching the heating element.

However, this current in the heating element creates heat and eventually rises up in temperature. When this happens, a “thermistor” (to be found inside the boiler) responds to the rising temperature and adjusts itself accordingly. This makes it possible for there to be an electronic feedback loop that then maintains a steady water temperature at the desired level.

Types of Thermostat
The most basic of thermostats are called “on-off”, these are found on low power heating appliances such as immersion heaters. They can be set to turn off when the water reaches a certain temperature and then turns back on when it drops too low again. This type of thermostat only has two settings, hot and cold.

Programmable thermostats are more common on larger heating appliances such as storage heaters and central heating boilers. The programmable version enables you to set a schedule in advance (setback) and it will switch your boiler on/off automatically at the times you choose. The schedules we use in the office are different from those we would use at home as the heating requirements are different. In the office, heat is required for part of the day but not all of it. At home, you tend to require heat 24 hours a day. The boiler does this by measuring the temperature in your house and turning itself on/off accordingly to maintain an even temperature.

What will make a thermostat to stop working?
If the monitor has been switched off, or there is a loss of power to the system (e.g. by switching off your fuse box), this could cause it not to respond correctly when you use the thermostat again.

Another common reason for this problem is that the batteries in your thermostat need to be replaced.

I’m having problems with my thermostat, what should I do?
 If your boiler isn’t responding to the thermostat you may need to re-sync it. To do this, simply press down on the program button until both sides of your display are illuminated. Once this has happened, release the program button.

You will then need to press the up or down arrow button on your thermostat, to change the temperature setting. Once you’ve changed it, make sure to save this new temperature by pressing the program button.

How do I reset my thermostat?
If you’re having problems with your thermostat it can sometimes be reset. To do this, simply press down on the program button until both sides of your display are illuminated. Once this has happened, release the program button.

You will then need to press the up or down arrow button on your thermostat, to change the temperature setting. Once you’ve changed it, make sure to save this new temperature by pressing the program button.

How do I know if my thermostat is broken? 
If your thermostat isn’t responding to the temperature that you have saved, then it might be broken. In this case, you should contact a reputable plumber or central heating engineer as soon as possible.

Can I fix my thermostat by myself?
We don’t recommend trying to fix your own thermostat. Most modern thermostats are complicated pieces of technology, so trying to fix them yourself could cause more damage than good. If you do decide you want to give it a go, make sure beforehand that you know exactly what type of thermostat you have. This way, should anything go wrong, you won’t end up replacing something that was actually working perfectly fine.

How much would it cost to replace a thermostat?
The cost of replacing your thermostat will depend on a number of factors. Larger, more complex thermostats are usually more expensive to replace than their smaller counterparts. The type of fuel you have could also affect the price, as some types are much harder to work with. If you’re concerned about the costs involved with replacing your thermostat, you should call a professional before starting the job as they will be able to give an estimation of costs.

How difficult is it to replace a thermostat?
The difficulty of replacing a thermostat depends on how experienced you are with DIY and plumbing. If you’re following a guide/instructions from a manufacturer, replacing a thermostat is usually fairly straightforward. If you’re going it alone, it might be harder to complete the job as you won’t have anyone there to guide or give advice throughout the process.

When you go about replacing your thermostat, make sure not to touch the boiler with the new thermostat. This is for safety reasons and could damage the boiler.