Cold Radiators, Slow Warmup Time and Noisy Central Heating Pipes ( A Look at Solutions)

By Daniel Woodley. Posted to the DIY blog of the popular Job Prices website. Updated May 2021.

It’s that time of year again where we start switching on our central heating systems and leaving them on for longer.

With that in mind, the team here at Job Prices recently updated our free cost calculator for central heating powerflushing.

Never Heard of Powerflushing?

Powerflushing is a process whereby water and chemicals are pumped through the radiators and pipes to loosen off and remove any sludge, limescale and rust.

Just look at the images below to see how clogged a system can become:

blocked heating pipe

Image courtesy: Best Heating

Limescale and sludge in pipe

Image courtesy of Nialls

Reduced flow through pipe

Image courtesy of Expert Powerflush

Once completed, the end result is a system that warms up quicker, has fewer cold spots on the radiators and rattles less.

As a cleaned system is more efficient, you can expect a modest saving on your heating bills too.

Check out our free cost calculator for powerflushing here (no email or signup is required).

Obviously, not every issue can be resolved with a powerflush. Below you’ll find a list of common winter problems you may encounter with your central heating system, we’ve also listed the most likely solutions too:

Common Winter Central Heating Problems and Solutions

Cold spots on radiatorsBleed the radiators, check water pressure and pump, powerflush the system or replace affected radiators. Try in that order.
Boiler whistling (similar sound to a kettle)Have the heat exchanger checked for limescale buildup, consider a water softener or electrolyte scale remover if you live in a hard water area
Boiler gurgling soundUnwanted air may have entered the system or the flow rate might be too low
Noisy radiators and pipes, gurgling soundsThe most likely cause is air trapped in the system. Try bleeding the air from the radiators in the home.
Boiler starts and then suddenly stops, possibly with various fault codes displayed on the screenThe condensate pipe, which is usually white and discharges waste water outside, may be frozen or blocked. This is a very common winter problem, and can be resolved by pouring warm water on the external pipe to melt the ice blockage. For internal condensate piping, check the exit point for blockages.
Humming sounds from pipes and radiatorsThe most likely cause is the pump, although a faulty immersion heater could be the culprit, have both checked by a professional
Knocking sound from pipes under floor boardsThis is often caused by pipes not being being secured correctly under the floor but could also be an issue with the central heating pump
Knocking sound from pipes when water taps are turned onThis is referred to as hammering and is often caused by pipes not being secured correctly under the floor boards. Trapped air and a faulty thermostat could also be the problem.
Slow radiator warm up timePossibly caused by air trapped in the system, try bleeding all the radiators. Also try balancing the radiators so warmup times are optimal. Limescale and sludge buildup will reduce the flow of the hot water through the system. Check thermostatc radoator valves are working, they should be warm either side f the valve when fully opened, replace as required. Try a powerflush.

Simple Checklist Before You Call a Pro

Many common winter problems can be resolved without the need to call a professional.

Try this checklist if you have a problem, it covers things anyone can check and doesn’t go beyond the basics:

  1. Check the condensate pipe isn’t blocked, possibly with ice if it’s been cold recently.
  2. Bleed the radiators to remove trapped air, a common problem found in systems that can cause lots of different noises, slow warm-up times and cold spots on radiators.
  3. Balance the radiators, it doesn’t take long and can improve warm-up times.
  4. Switch the system off and allow it to fully cool. Switch back on and wind the thermostat up to the maximum. You should hear a clicking sound, if you don’t, you may have a faulty thermostat.
  5. Check for dampness under radiator valves, especially if you have recently adjusted them. Old valves are prone to leaking.
  6. Check the pipes on either side of any radiator thermostat valves, they should both be warm. If fully opened and still cool, replace the valve as it may be faulty.
  7. Check the pilot flame on the boiler (if you can see one) for consistency of colour and size.
  8. Check programmer has power.

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This guide was written by and was last updated in May 2022.

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Author - Danny Woodley