Radiator Faults

Bleeding Radiators	Central Heating Set Up	Pipe Insulation
Radiator Efficiency	Radiator Faults	Thermostatic Radiator Valves

There are many reasons why one or more radiators in a house are cold, 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. 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.

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 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 up 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 they are insulated by 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.

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.

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)
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 Doesn't Get Hot Enough

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

Noises From One Or Several Radiators

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