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My TRV Is Faulty!?

Faulty TRVThermostatic radiator valves (referred to as TRVs) are often used in hot water central heating systems to control the temperature of individual radiators. Apart from getting the room temperature as you want it setting these valves correctly can lead to big savings in heating costs. They work by gradually turning off the hot water flow to the radiator as a room reaches the desired temperature. Normally there is one room without a TRV (usually a bathroom); this is to ensure can always be a flow of water round the system. Unfortunately it is often the case these valves are not set or not working properly leading to rooms being too hot or too cold.

TRVs work best when there is free air circulation around both them and the radiator. It is important that thermostatic radiator valves are not in a draught which will have a big and variable effect on operation. Also vital is making sure they are not obstructed by hanging curtains, clothes or furniture in front of or over them. Once a room has reached the temperature set the radiator will be somewhat cooler than when the room is warming up, this is not a fault. Always check out the simple things before thinking the worst and calling a plumber. Below is a list of the common TRV faults plus some simple tips for fixing the problems.

More simple heat saving tips can be found at Practical Home Energy Saving.

Thermostatic Radiator Valve Faults

Room is too hot or too cold

  • Valve incorrectly adjusted – adjust
  • Room thermostat overriding TRV setting – reset room thermostat

Radiator is always on

  • Valve is fully open – adjust
  • The valve is in a draught – stop draught
  • Airflow is blocked by furniture or other objects – remove items
  • The thermostat head assembly is loose on the thermostatic valve body – tighten

Radiator is always off

  • Valve fully closed – adjust
  • The TRV head is clogged with dust and dirt stopping airflow – vacuuming fixes

Unable to adjust the TRV to give the correct room temperature

  • Airflow around the valve is blocked by furniture or other objects– remove items
  • The TRV head is clogged with dust and dirt reducing airflow – vacuuming fixes
  • The thermostat head assembly is loose on the thermostatic valve body – tighten

Adjusting Thermostatic Radiator Valves

The most common cause of a TRV not working is because it is incorrectly set or turned off. The valve is set by turning the control knob to set the desired room temperature. Anticlockwise increases the temperature and clockwise reduces it. Since rooms can take a long while to reach temperature setting these valves correctly isn’t a quick process. The best way is to do it for each room over several days, before adjusting the valve run the heating for a few hours to make sure it has stabilised. If the room is too hot screw the valve clockwise one mark and check the temperature again the next day. Unscrew the valve one mark if the room is too cold. Repeat this daily until the temperature is correct.

The temperature markings on these valves do not represent specific room temperatures because the temperature at which the valve operates depends on the air flow around the valve, the water temperature, the size of the room and the losses through walls, windows, doors, floors and ceilings. It is quite normal to have very different settings for the same temperature in different rooms because of this. If there is more than one radiator heating an area there will be an interaction between them. To set the valves in this case start with all the valves in the room on the same setting and then if the room temperature is not even try adjusting the one adjacent to the coldest part of the room. This can be a bit fiddly and take time. Once this has been done they can be adjusted together to get the right room temperature.

Blocked Airflow

Often TRVs fail to work properly because either the valve or the radiator has poor air circulation. The cause is often furniture such as settees or book cases in front of the valve and radiator, furniture should ideally be at least two feet away from the radiator and valve. Another common cause is things hanging over the valve or radiator blocking the airflow such as clothes or towels, removing these will make a big difference. Over time the head assemblies of these valves can become clogged with dust and dist, regular vacuuming around the valve and the slots in the head assembly will stop this problem. The gap between the floor and the bottom of the radiator should always be totally clear of obstructions.


If thermostatic radiator valves are in any sort of draught they will fail to operate correctly giving variable room temperatures. Radiators are often mounted below windows which can be a major source of draughts, fixing these will not only enable the room temperature to be controlled more accurately it will also save money on the heating bills. Open doors are another source of draughts which means that draughts in adjoining rooms need to be identified and fixed too.

Confusion between Room Thermostats and TRVs

If a room thermostat is in a room with radiators fitted with thermostatic valves you will need to decide which is going to control room temperature, often the room thermostat will also turn off the heating to the whole house when its set temperature is reached,. The best compromise if not all radiators have thermostatic valves is to set the thermostatic valves for slightly higher than the desired room temperature and then the room thermostat to the desired room temperature. If all radiators have thermostatic valves it is not worth bothering setting the room thermostat, in this case set the room thermostat to its the maximum temperature.

Other Problems

Although much less likely there are other faults that can stop TRVs working properly or possibly there is a faulty radiator.  Thermostatic radiator valves will also not work properly if the central heating system is not balanced.

Removing sludge from your Central Heating System

Sludge deposits can cause your central heating system to work inefficiently or worse still, stop working at all. The sludge is created over time as the metal within the radiators and pipework in a property, is corroded and reacts with the oxygen in the air. As a result a build up of thick black sludge is extremely common place in heating systems across the UK.

Sadly a lot of insurance companies won’t insure your combi boiler or central heating system against any damage caused by this build up. As one of the most common causes of boiler breakdown and system in the UK, there are a few ways to resolve this. However, if you want to avoid a full system flush, the most cost efficient way to remove the sludge from your boiler system is to use a filter.

One of the best products out there to do this is currently the Magnaclean whose mantra is “Prevention is Better Than the Cure


Magnaclean FilterHow does a Magnaclean work?

A Magnaclean is a filter that is fitted on the return pipework that leads to the central heating system.

The Magnaclean filter removes sludge deposits that are present in the water as it pumps through your system. Removing this sludge is beneficial for a number of reasons:

  1. Reducing fuel consumption
  2. Reducing system wear and tear
  3. Reducing boiler breakdowns and the hassle and hardship they cause.

These features combined mean the return on investment for a Magnaclean Filter is much faster than other energy efficiency/maintenance devices.

Sludge deposits are one of the most common causes of boiler breakdown and system wear and tear and Magnaclean works by removing this.

Why can fitting a Magnaclean Filter be beneficial?

There are many benefits to proactively fitting a Magnaclean to your system. Firstly, it is obviously a lot better to deal with potential irregularities in your central heating system before they escalate to something more serious. By cleaning your heating system, you can stop the build-up of sludge in your pipework and radiators before it stops these things working as they should do.

As the Magnaclean can capture the sludge deposits at a quicker rate than they are deposited in the system, the Magnaclean filter does a great job at maintaining your system. In the long term this can help your heating system to last 60-80% longer it would do otherwise.


Alternatives to A Magnaclean Filter…

A lot of large heating and plumbing companies will recommend a powerflush as the only way to deal with the build up of sludge in our heating system. The truth is that a powerflush would help, but it is costly and isn’t something that is typically covered in the cost of your monthly boiler & heating cover plans. You are therefore likely to have to pay a lot to have this service carried out by a qualified plumber or heating engineer.

You can be proactive and try and avoid this expense. Having a filter such as the Magnaclean, or alternatives such as the Sentinel Sludge Remover or the Fernox Central Heating Protector, can enable you to minimise the build up of sludge in your system, meaning you reduce the likelihood of being affected by performance issues going forward.


Where to buy?

Direct Heating Supplies sell all the heating and plumbing supplies you need at great low prices with next working day delivery.


by Tom Key