If you have a central heating system sooner or later you’ll experience issues with downstairs radiators. You may be tempted to call an expensive plumber immediately, which could be a big waste of money as many problems can be fixed at home.

When downstairs radiators stop working the most likely cause is a broken water pump. Upstairs radiators may still become hot due to hot water naturally rising. Other common causes are related to trapped air and sludge built up in the system which is fixable without a plumber.

When your upstairs radiators become hot but your downstairs don’t, what should you do? Follow these 6 simple steps to fix or diagnose your problem…

1. Check for thermostat issues

The thermostat could be causing your downstairs radiators to remain cold. Radiators commonly have a TRV (Thermostatic Radiator Valve) which controls the temperature of each radiator.

Sometimes the TRV becomes trapped in a closed position. When this happens on a radiator, all the hot water will be flowing to other areas within the house. If turning the plastic valve to the highest number isn’t possible, remove the plastic head to access the metal screw underneath.

Whilst this may be the cause of an individual radiator staying cold, it’s unlikely to be the cause of your entire downstairs radiators malfunctioning. However, the other way radiators are controlled is via an electronic thermostat such as this one:

Where an electronic thermostat controls the entire downstairs, check for any potential issues such as dead batteries or faulty wiring. Check out this article for troubleshooting the most common thermostat issues.

If an electronic thermostat has stopped working this may well be the cause of downstairs radiators not heating up.

If the thermostat is not causing the issue, move on to step 2…

2. Look into pressure issues

In order for radiators within a closed central heating system to heat up correctly, water pressure needs to be distributed evenly across all the radiators within the home.

The diagram below shows how water gets heated and pumped around radiators via the boiler and water pump.

A lack of water pressure could be causing your downstairs radiators not to work. This is because water flow won’t be pressurized enough to distribute heat from the source i.e. the boiler to downstairs radiators.

The first thing to check is the water pressure on your boiler:

Locate the pressure gauge on your boiler. It’s normally at the front of the boiler and will show a number. The needle should usually be at between 1 and 2 bar (normally shown in green) but double-check your manual for the correct pressure.

If your pressure is too low you’ll need to top it up. The good news is that this is an easy and quick task to complete by following these steps:

Once you’re confident that your boiler is operating at the correct pressure, turn it on and see if the radiators heat. If no luck, move on to step 3.

3. Air lock or blockage in pipes

Once you’ve ruled out the thermostat and boiler pressure being the cause of cold downstairs radiators, the next thing to check is whether there’s an airlock somewhere in your system. This is especially likely if your radiators are fed by droppers from upstairs.

An airlock could prevent hot water from reaching the downstairs portion of your HVAC.

Easiest solution

The easiest way to force out a blockage from the pipes is to shut off all of the radiators that are working. This will send pumped water to those radiators that don’t work, and it could fix the problem. Air would be forced out, eliminating the air block and therefore allowing hot water to reach all radiators.

You achieve this by closing the lockshield valve on all the upstairs radiators (or any radiators that do work).

The lockshield valve looks like this:

There will be a spindle under the plastic cover which should be turned clockwise.

If your downstairs radiators start to work after turning your boiler on, you may be in luck and the air has been forced out of the system.

Bleeding the radiators

If this isn’t successful, you should move on to bleeding the downstairs radiators. ‘Bleeding’ means to remove trapped air inside your heating system. One common sign that a radiator needs bleeding is where the bottom part of the radiator is hot but the top is cold.

Bleeding a radiator is done by locating the bleeding valve on the top of the radiator and opening the valve using a radiator bleeding key or a flat head screwdriver. Screwing anti-clockwise releases trapped air and the valve should be left open until water starts dripping out.

Before you bleed the downstairs radiators, shut off the upstairs radiators (both the lockshield valve and the thermostatic valve) which may force heat downwards.

Once the upstairs radiators are shut off, work your way through the downstairs radiators. To bleed, leave the lockshield valve fully open on the radiator you’re bleeding and turn the thermostatic radiator valve off. Open the bleeding valve and let the water run into the container for 5 minutes. Have a second person topping up the boiler water pressure whilst this is happening.

Work your way systematically through each downstairs radiator. You’ll know bleeding has been successful when you hear spluttering and air coming through the valve.

This is a helpful video demonstrating bleeding:

Hopefully removing blocked air from your radiators solves the issue. Try turning the central heating on again and waiting a few minutes to test.

If not, move on to step 4: balancing the radiators.

4. Balance Your radiators

Sometimes radiators need re-balancing to prevent certain radiators from getting all the available heat.

Most HVAC systems have a water pump that pumps hot water to all available radiators. However, hot water naturally gravitates upwards and stays upstairs before making its way back to the boiler. When the system isn’t balanced correctly, hot water will therefore naturally rise and the upstairs radiators will get heat whereas the downstairs radiators won’t.

By balancing the radiators, you can make sure all radiators within the home get an equal distribution of heat.

Balancing is achieved by adjusting radiator valves.

Note: Radiators must have been bled before attempting balancing.

1. Make sure central heating is turned off, and allow your radiators to completely cool.
2. Open the lockshield valve completely on all downstairs radiators. This is achieved by manually turning the valves on all radiators all the way anti-clockwise.
3. Fully close the lockshield valve on all upstairs radiators. Then go to each upstairs radiator and only open the lockshield valve a quarter of a turn.

Here is a helpful video on how to balance radiators:

Test if balancing the radiators has been effective in allowing more heat flow to your downstairs radiators. If not, move to step 5…

5. the circulator pump

The circulator pump is responsible for circulating hot water from your boiler through your central heating system. If hot water is still only reaching your upstairs radiators and not your downstairs radiators, the most likely issue is a faulty circulator pump.

Note: if your downstairs radiators get some heat at the top but stay cool at the bottom, you may be experiencing a sludge build-up and you should read step 6.

When the pump fails, the upstairs gets hot due to gravity circulation whereas the downstairs radiators will not heat.

These pumps often freeze up, seize up, and therefore don’t move water. Even if the pump does need replacing it isn’t the end of the world – the average cost (including labor) for a new pump is £150 – £300.

Aside from upstairs radiators not working, other signs of a broken circulator pump are:

• Strange noises coming from the boiler such as a buzz or hum
• Water leaking from the pump
• The pump is very hot to touch
• The pump will not switch off
• The pump is not switching on i.e. no vibration or heat

After ruling out many other issues, most homeowners at this stage will call a qualified plumber to come out and fix or replace the boiler pump. The below is meant for informational purposes only, and this is a job best left to qualified plumbers.

However, there are some other checks you may be curious to go through in order to determine the exact fault.

The circulation pump is usually located in or near your boiler, especially in combi-boilers.

The circulation pump is located near the boiler

check the pump for an airlock

Like the HVAC system itself, trapped air within a circulation pump can cause it to stop working. Typically where this happens you’ll hear strange noises coming from your boiler pump.

In order to fix this, air needs to be released by adjusting the bleed screw. You’ll need a screwdriver and something to clean up water with.

This process is similar to bleeding radiators in that we unscrew the bleed valve, allow trapped air to get out, and then re-tighten.

You’ll want to ensure you’ve switched off the electrical supply to the pump before you begin any kind of work on the water pump.

Place a towel under the screw to absorb leaking water. Turn the small bleed screw on the pump anti-clockwise very slowly to allow trapped air to escape.

Re-tighten the screw and turn the electrical supply back on.

Check if the pump has any power

If your boiler has power but your pump does not, it could be a variety of issues relating to the wiring or the fuse.

Check whether your pump has power by listening to the pump. It’s likely to make a whirling noise if powering up. Also, feel the pump – it should be vibrating and slightly warm.

Unfortunately, this isn’t a fix that should be attempted at home. A gas safe engineer will need to come out and check the wiring for you. If the wiring or fuse can’t be fixed it’s likely you’ll need a new pump.

Incorrect speed on the circulation pump

Incorrect flow rate settings could be causing issues with your downstairs radiator. This could be the case where your pump is weak or breaking.

Whilst it’s possible for homeowners to adjust the settings of circulation pumps, we wouldn’t recommend it. Many pumps only have settings of 1, 2, and 3, and having the pump set to the wrong setting could damage the boiler.

It’s certainly worth calling an engineer for their advice if you expect a weak circulation pump.

6. the last possible issue: sludge build-up

Sludge build-up is caused by air and water reacting with the metal in your central heating system. A sludge build-up may be the cause of downstairs radiators not heating up fully. They may still heat up slightly, and the problem may have worsened over time.

Sludge (magnetite) is heavier than water so often settles in the radiators and pipework on the ground floor. Sludge will often cause radiators to heat at the top but stay cold at the bottom.

Sludge will restrict the flow of water as it blocks pipes. If left untreated, it can also cause many issues and even break your boiler and pump.

If you notice downstairs radiators stay particularly cold at the bottom, it may be worth either paying a gas-safe engineer to do a power flush or attempting to clean your radiators at home yourself.

This is achieved by removing problem radiators and cleaning them using your garden hose. This is quite a time-consuming and messy task but it may be worth attempting before contacting a plumber.

Here is a video showing how to remove radiators and clean sludge:

Once downstairs radiators have been cleaned and replaced, try turning your central heating back on. Hopefully this has fixed the issue and will also prevent future damage to your HVAC system.

Final thoughts

Where you have multiple radiators downstairs and none of them are getting any heat one likely cause is a faulty circulator pump. Before calling a plumber, it is certainly worth running through checks relating to the thermostat, pressure, blockages, and balancing.

Whilst skilled DIYers may be able to fix boiler pumps more often than not this is a job best left to professionals. The good news is that this is a simple job for a plumber and shouldn’t cost you more than £300.

Other related and useful articles

How To Repair A Leaky Radiator Bleed Valve Quickly And Easily

When To Replace A Boiler