Why do my upstairs radiators get hot but the downstairs ones stay cold?

This is one of the most common heating complaints and it almost always has the same answer: the system has never been balanced. Water takes the easiest path, and on most houses that path goes upstairs.

What you'll need

• A bleed key and a cloth
• A small spanner for the lockshields
• Optionally a thermometer or an infrared thermometer

Step by step

1. Check the obvious things first.Every downstairs TRV fully open, the room thermostat well up, the programmer calling for heating, and the boiler firing. Rule those out before touching anything.
2. Bleed the whole system, ground floor first.Air anywhere reduces circulation. Bleed downstairs radiators before upstairs, then top the pressure back up if it is a sealed system.
3. Check every downstairs TRV pin.Take each head off and press the pin. One seized pin explains one cold radiator; several explain a cold floor.
4. Feel which radiators are hottest.Upstairs scorching and downstairs lukewarm is the classic unbalanced pattern, and it tells you the fix is balancing rather than repair.
5. Balance by throttling the favoured radiators.Close the lockshields on the hottest upstairs radiators by a turn or two at a time. That forces more water downstairs. Allow twenty minutes between adjustments.
6. Do it properly if you want it right.Open all lockshields, then close them all, then reopen each by a set amount starting from the radiator nearest the boiler and working outwards, checking the temperature drop across each.
7. Check the pump speed.Most circulating pumps have a three-speed switch. If it has been left on the lowest setting, the far and low parts of the system suffer first. Step it up one setting and observe.
8. Consider sludge if a radiator is cold along the bottom.Downstairs radiators collect sludge first because it settles. Cold along the base means flushing, not balancing.
9. Check whether the system is genuinely undersized.If everything is balanced and the boiler runs continuously without reaching temperature, the radiators or the boiler may be too small for the house — a different conversation.
10. Record what you changed.Write down the lockshield turns on each radiator. It makes the next adjustment straightforward instead of guesswork.

Tips

• Balance with the system fully hot and give it twenty minutes between changes. Rushing it makes it impossible to judge.
• An infrared thermometer makes balancing far easier — aim for a similar temperature drop across every radiator.
• If the pump is on its lowest speed, that alone can be the whole problem on a larger house.

Common mistakes

• Opening all the lockshields fully — Water then takes the shortest, easiest route back to the boiler, which is nearly always upstairs. Balancing works by deliberately restricting the easy paths.
• Turning the boiler temperature up to compensate — It makes the favoured radiators hotter without changing the distribution, so the cold rooms stay cold and the fuel bill rises.

If it doesn't work

Questions people ask