Radiator Installation & Repairs

Why it happens: Usually the pin inside the thermostatic valve (the one with the numbers) has stuck down, so no hot water can get in. It can also be air, or a valve that’s been turned off.

Try this first: Check the valve isn’t on 0 or the snowflake. Unscrew the numbered head and gently tap the small metal pin underneath. It should spring up. Then bleed the radiator. Turn the heating off and let the radiator cool. Hold a cloth under the small square screw at the top, turn it a quarter turn with a radiator key until the hissing stops and water appears, then close it.

What we do: Free the pin or fit a new valve head, usually in one short visit. Repairs from £100.

Why it happens: Hot water is reaching the radiator but can’t get through. The valve is stuck shut or the radiator is blocked with sludge.

Try this first: Check the pin as above. If it moves freely and the radiator stays cold, it’s a blockage.

What we do: Free or replace the valve, or take the radiator off and flush it out. Repairs from £100.

Why it happens: Hot water isn’t reaching it at all. The plain valve under a cap at the other end (the lockshield) may be shut, there may be an airlock, or the pipe is blocked.

Try this first: Pull the cap off the lockshield. If it’s turned fully clockwise, open it two turns anticlockwise.

What we do: Reset the valves, clear the airlock or blockage and balance the radiator back in. Repairs from £100.

Why it happens: It gets whatever hot water is left. If the system isn’t balanced, the radiators nearest the boiler take it all.

Try this first: Turn the numbered valves down a little on the radiators that heat up first and see if the last one improves.

What we do: Balance every radiator so they all heat at the same rate, and check the pump is strong enough. Repairs from £100.

Why it happens: Towel rails are tall and thin, so air collects at the top, and they’re often last on the system. If yours also has an electric element, the element may have failed.

Try this first: Bleed it and check both valves are open. Turn the heating off and let the radiator cool. Hold a cloth under the small square screw at the top, turn it a quarter turn with a radiator key until the hissing stops and water appears, then close it.

What we do: Bleed, balance or replace the valves, or swap the element on a dual fuel rail. Repairs from £100. New towel rails fitted from £120.

Why it happens: Sludge. Rusty water settles at the bottom and blocks the flow.

Try this first: Bleeding won’t help with this one.

What we do: Take the radiator off and flush it. If several are the same, a powerflush clears the whole system from £299, and a magnetic filter stops it coming back.

Why it happens: A slightly cooler bottom is normal, as the water cools on its way through. If it’s properly cold and the radiator is new or has just been flushed, a valve is only part open or the water is going in the wrong end.

Try this first: Check both valves are fully open.

What we do: Check the valves and pipework and balance the radiator. Repairs from £100.

Why it happens: Air. It rises and sits at the top.

Try this first: Bleed it. Turn the heating off and let the radiator cool. Hold a cloth under the small square screw at the top, turn it a quarter turn with a radiator key until the hissing stops and water appears, then close it. Then check the boiler pressure. Look at the pressure gauge on the front of the boiler. With the heating off it should read between 1 and 1.5 bar. If it’s under 1, top it up using the filling loop, following your boiler manual.

What we do: If it keeps needing bleeding, air is getting in somewhere. We find where and fix it.

Why it happens: Water is only getting part way across. A valve is part closed, or sludge is blocking the middle.

Try this first: Check both valves are fully open.

What we do: Free or replace the valve, or flush the radiator. Repairs from £100.

Why it happens: The heating dial on the boiler may be set low, the system may be out of balance, or sludge and a tired pump are slowing everything down.

Try this first: Turn up the heating dial on the boiler (not the hot water dial) and check the numbered valves aren’t turned down.

What we do: Balance the system, test the pump and flush out any sludge.

Why it happens: The radiator is too small for the room, or a sofa or long curtains are trapping the heat. Draughty windows and doors make it worse.

Try this first: Pull furniture away and tuck curtains behind the radiator.

What we do: Work out how much heat the room needs and fit a bigger or double panel radiator if it needs one. New radiators fitted from £120.

Why it happens: Air, sludge or a system out of balance. Which ones are cold, and where, usually tells us which.

Try this first: Bleed the cold ones and check the boiler pressure. Look at the pressure gauge on the front of the boiler. With the heating off it should read between 1 and 1.5 bar. If it’s under 1, top it up using the filling loop, following your boiler manual.

What we do: Balance the system. If several are cold at the bottom, a powerflush from £299.

Why it happens: Sludge settles in the lower radiators, the system is out of balance or the pump is weak. In homes with separate upstairs and downstairs heating, the valve for downstairs may have stuck.

Try this first: Check the downstairs numbered valves aren’t turned down.

What we do: Balance, flush, or repair the pump or valve.

Why it happens: Air rises to the highest radiators, and low boiler pressure means the water can’t push up to the top floor.

Try this first: Check the boiler pressure. Look at the pressure gauge on the front of the boiler. With the heating off it should read between 1 and 1.5 bar. If it’s under 1, top it up using the filling loop, following your boiler manual. Then bleed the upstairs radiators.

What we do: If it keeps happening, we find where the pressure or air is being lost, and check the pump.

Why it happens: Usually the boiler isn’t being asked for heat, the pressure is too low, or the pump or a valve has failed.

Try this first: Turn the room thermostat up a few degrees, check the timer is set to heating, and check the pressure.

What we do: Find the fault and fix it, at a fixed price before we start. More on our No Heating page.

Why it happens: A combi boiler has a valve inside that switches hot water between your taps and your radiators. If it sticks on taps, you get hot water but cold radiators. If you have a hot water cylinder, a motorised valve on the pipes near it does the same job and may have failed.

Try this first: Check the thermostat and timer are asking for heating.

What we do: A Gas Safe engineer repairs or replaces the valve. More on our No Heating page.

Why it happens: The same valve, stuck the other way, sending all the hot water to the radiators.

Try this first: Check the hot water timer is on.

What we do: Repair or replace the valve. More on our No Hot Water page.

Why it happens: The valve that directs the hot water is stuck open, so hot water gets into the radiators whenever you run a tap or heat the cylinder.

What we do: Replace the valve, usually in one visit.

Why it happens: If water came out straight away, it wasn’t air. It’s a stuck valve or sludge.

Try this first: Check the valve pin (see One Radiator Not Working, the Rest Are Fine).

What we do: Free or replace the valve, or flush the radiator. Repairs from £100.

Why it happens: Bleeding lets water out, the pressure drops below 1 bar and the boiler shuts down to protect itself.

Try this first: Top up the pressure. Look at the pressure gauge on the front of the boiler. With the heating off it should read between 1 and 1.5 bar. If it’s under 1, top it up using the filling loop, following your boiler manual. Then press reset on the boiler.

What we do: If it won’t hold pressure, there’s a leak somewhere. We find it and fix it.

Why it happens: If nothing comes out, the pressure is too low or the bleed screw is blocked with paint or sludge. If cold water comes out, the radiator is full but hot water isn’t reaching it.

Try this first: Top up the pressure and try again.

What we do: Clear or replace the bleed screw, or find the blockage. Repairs from £100.

Why it happens: The valves aren’t fully open, there’s air from filling up, or it hasn’t been balanced in, so the older radiators take the water.

Try this first: Check both valves are fully open and bleed it.

What we do: Every radiator we fit is bled and balanced before we leave. If someone else fitted yours, we’ll sort it. Repairs from £100.

Why it happens: Draining and refilling puts air in the system, a new boiler can stir up old sludge, and the radiators may need balancing to the new boiler.

Try this first: Bleed every radiator and check the pressure.

What we do: Bleed, balance and check the filter, and powerflush if the old sludge is the problem.

Why it happens: Water was lost when the radiator came off, so the pressure dropped and air got in.

Try this first: Make sure both valves are closed, then top up the pressure and bleed the other radiators.

What we do: Cap the pipes properly, refill and bleed the system, or move or remove the pipework for good.

Why it happens: The seal inside the valve is worn or the nut has worked loose, often from the heating going on and off.

Try this first: Hold the valve body steady with one spanner and tighten the nut a quarter turn with another.

What we do: Reseal or replace the valve on the spot. Repairs from £100.

Why it happens: If it drips from the joint where the valve meets the radiator, the joint can be fixed. If it’s coming from the metal itself, the radiator has rusted through from the inside.

Try this first: Dry it with a towel and watch where the drip forms.

What we do: Fix the joint, or replace the radiator like for like. New radiators fitted from £120.

Why it happens: A loose joint or a pinhole in the pipe. If the pipe runs under the floor you may only see a damp patch or a stain on the ceiling below.

Try this first: Close both valves and switch the heating off.

What we do: Find and repair the leak. More on our Water Leak Repair page.

Why it happens: The bleed screw isn’t fully closed or its seal has worn. If it’s coming from the metal, it’s rust.

Try this first: Gently close the bleed screw with a radiator key.

What we do: Replace the bleed screw, or the radiator if it’s rusted through.

Why it happens: Radiators rust from the inside out. Once there’s a hole it can’t be properly repaired.

What we do: Replace it like for like, usually the same day, from £120. If the rest of the system is rusting too, a powerflush and magnetic filter protect the other radiators.

Why it happens: Sealant and patches are a temporary fix at best. Sealant poured into the system can block the boiler and valves, which costs far more than the leak. Replace the valve or radiator instead. Valve repairs from £100.

What we do: Replace the valve or radiator instead. Valve repairs from £100.

Why it happens: The numbered thermostatic head has failed, or the pin underneath has stuck.

Try this first: Take the head off and tap the pin (see One Radiator Not Working, the Rest Are Fine).

What we do: Fit a new head or valve. Smart valves such as Tado or Hive can be fitted too. Repairs from £100.

Why it happens: It’s seized from sitting in one position all summer, or the head is broken.

Try this first: Don’t force it with pliers. You can snap the valve and cause a leak.

What we do: Free it or replace it. Repairs from £100.

Why it happens: Old manual valves can be swapped for thermostatic ones so each room controls itself.

What we do: Drain down only what’s needed, fit the new valve, refill and bleed. From £100.

Why it happens: Balancing sets how much hot water each radiator gets, so the ones nearest the boiler don’t take it all. It’s done by adjusting the lockshield valves and checking each radiator’s temperature. You can do it yourself but it takes time. We balance a whole house in a short visit.

What we do: We balance a whole house in a short visit.

Why it happens: Tall radiators trap air at the top and collect sludge at the bottom, and many designer radiators give out less heat than a standard panel of the same size.

Try this first: Bleed it and check both valves are open.

What we do: Bleed, flush or balance it, and check it’s big enough for the room. Designer radiators fitted from £120.

Why it happens: A heat pump runs the water cooler than a boiler, so radiators feel warm rather than hot. That’s normal. If the rooms don’t reach temperature, the radiators are too small for a heat pump.

What we do: Check each room and upsize the radiators that need it. We're MCS certified for heat pump work.

Why it happens: The valve that splits hot water between the underfloor and the radiators has stuck, or the controls are only calling for the floor.

What we do: Repair the valve or controls. More on our Underfloor Heating Repair page.

Why it happens: Years of sludge, or rust inside the panel.

What we do: Flush it if it’s sound, or replace it like for like from £120 if it’s rusting through.