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Faulty radiators

There are many reasons why one or more radiators in a house are cold or lukewarm, use the information here to identify the areas for investigation .Please read through all the possible diagnosis before jumping to conclusions. Always check the simple reasons first before looking for expert assistance as they are often the most likely cause. Often the cause is simply due to thermostatic radiator valves (TRVs) being turned off or incorrectly set. The information here makes the fundamental assumption that the system did work properly at some stage, if not then you are into investigating the design which is beyond the scope of this page. Whenever radiators are not working properly the heating system is not running at maximum efficiency which means there are opportunities to cut heating costs.

 

Heating systems are sometimes zoned to enable different parts of the house to be heated to different temperatures e.g. split between upstairs and downstairs. Where this is done there are zone control valves to manage the water flow depending on the room temperatures or time switch settings. in this case there is likely to be a room thermostat and/or time switch setting for each zone.

 

If the rooms are reaching the desired temperature and the thermostatic valves are cutting off the flow it is likely that all the radiators will be at different temperatures. It all depends on how hard the radiator is working to maintain the temperature. The hotter the temperature the less the thermostatic valve is closing. How hard a radiator works depends on the size of room being heated, the size of the radiator, how high the thermostatic valve is set, how well insulated the room is and how often any external doors are opened and closed. Generally downstairs radiators will be cooler as the rooms are insulated by any heated rooms above. If there is a very large difference and no other factors that affect this it may be worth looking at whether the loft insulation can be improved to reduce heat loss through the ceilings and cavity wall insulation to reduce heat loss through the walls.

 

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It is worth noting that radiators are likely to be slightly hotter at the top than the bottom, how much will vary from system to system, room to room, the design of the radiator and the airflow around it. As long as the difference is no worse than the drop across the radiator this is not an indication of a problem.

 

Firstly establish whether the problem affects one radiator or several to help narrow down the choices. We have tried to put the faults in each section in order of how likely they are to be the cause.

One Radiator Is Cold

 

Thermostatic valve turned off - turn anti clockwise to open

Thermostatic valve cut off because room temperature higher than setting - turn anti clockwise to increase temperature

Seized thermostatic valve - caused by scale build up - tapping the control pin may fix (see thermostatic valves)

The thermostat in the thermostatic valve head assembly has failed

Flow (lock shield) valve turned off - less likely if the system was working

Airlock in pipe work - often where the radiator is below the level of feeding pipes

Blocked thermostatic valve - caused by scale and sludge in the system

Blocked flow (lock shield) valve - caused by scale and sludge in the system

Blocked pipe feeding the radiator - caused by scale and sludge in the system

One Radiator Is Too Hot

 

Seized thermostatic valve - caused by scale build up - tapping the control pin may fix (see thermostatic valves)

The thermostat head assembly is loose on the thermostatic valve body

Seized thermostatic valve - caused by scale build up - tapping the control pin may fix (see thermostatic valves)

The thermostat in the TRV head assembly has failed

One Radiator Doesn't Get Hot Enough

 

Thermostatic valve cut off because room temperature higher than setting - turn anti clockwise to increase temperature

Airflow around the TRV is blocked by hanging clothing, furniture or a radiator cover

Partially blocked thermostatic valve - caused by scale and sludge in the system

Partially seized thermostatic valve - caused by scale build up - tapping the control pin may fix (see thermostatic valves)

Partially blocked flow (lock shield) valve - caused by scale and sludge in the system

Partially blocked pipe feeding the radiator - caused by scale and sludge in the system

One Radiator Is Cold At the Top

 

Air in the radiator - bleed the radiator (see bleeding radiators)

Low water level in the radiator - usually highest radiator in the house - caused by low water level in system

One Radiator Is Cold At The Bottom

 

Build up of sludge in the bottom of the radiator - usually in radiators fed from above - flushing system may fix

One Radiator Only Is Hot

 

All thermostatic valves turned off

All Radiators Are Cold

 

Controller/Time switch not switching on at the correct time

Hot water heating only selected on the controller

Room thermostat set too low

Boiler not working

Circulation pump failed

Controller/Time switch has failed

Several Radiators are Cold

 

Controller/Time switch not switching zone on at the correct time

Zone control valve switched off at the controller

Zone control valve failed

Airlock in pipe work - often where radiators are below the level of feeding pipes

Controller/Time switch has failed

Downstairs Radiators Are Cold, Upstairs Radiators Are Hot

 

Controller/Time switch not switching zone on at the correct time

Zone control valve switched off at the controller

Zone control thermostat set too low

Pump switched off

Zone control valve failed

Pump failed

Controller/Time switch has failed

Downstairs Radiators Are Hot, Upstairs Radiators Are Cold

 

Controller/Time switch not switching zone on at the correct time

Zone control valve switched off at the controller

Zone control thermostat set too low

Zone control valve failed

Low water level in the system - could be a stuck cistern valve

Controller/Time switch has failed

Radiators Furthest From The Boiler Are Cold

 

System needs setting up and balancing

All Radiators Don't Get Hot Enough

 

Room thermostat set too low

Boiler thermostat set too low

Pump switched off

Pump failed

Boiler thermostat has failed

Build up of sludge in the system - flushing system may fix

All Radiators Are Cold

 

Pump switched off

Pump failed

Some Radiators Are Warm When Water Heating Only Is In Use

 

A design fault rather than a fault as such. The pump isn't running but some radiators get warm - only option turn off radiators

Failure of a zone control valve

Failure of the main heating control valve

Noises From One Or Several Radiators

 

Air in the radiator or adjacent pipes - usually easy to solve by bleeding the radiator

Thermostatic valve(s) fitted wrong way round - usually happens when the system stabilises - opening one valve fixes temporarily

Boiler thermostat set too high - try turning it down (not the room thermostat)

Low water level caused by lack of water in the system - could be a stuck cistern valve

Low water pressure in closed systems

Scale and sludge in the radiators and pipes

Failed pump bearing sometimes manifests itself as noise from the radiators

One Or More Radiators Need Bleeding Regularly

 

Low water level in the system - could be a stuck cistern valve

Bleed process incomplete or large amount of air trapped in the pipes

Air leak in system