Hot water, but cold radiators or cold water, but hot radiators

If all of the radiators are cold all over, read on. If the radiators are just cold at the top, check out the next question, below, and our tips for bleeding radiators.

If only one tap doesn’t give hot water, check that tap to see if it’s blocked or needs a new washer. If all hot water taps are cold read on.


Before you do anything else, check your thermostat. This is a small dial located on the wall somewhere around your house. It has a temperature scale, generally from 0 to around 30, which allows you to set the desired ambient temperature. Check the dial and turn it to 17-20 degrees. Check if the radiators begin to warm up.

If they don’t, follow these steps:


Step 1

Find your Programmer. This will be mounted on the wall, often in the kitchen, bathroom or airing cupboard, and is an electrical device with an in-built clock which allows you to programme when your heating is switched on and off. Check that both Central Heating (CH) and Hot Water (HW) are switched on. You may have to override the timer to do this.


Step 2

If this doesn’t work, check the motorized diverter valve, which you can find next to your boiler. If you are not sure what the unit looks like, have a look at this. This is a small valve which controls the flow of hot water to the boiler and the central heating system. The valve prioritises water supply – during the day it normally gives priority to hot water, as this is usually needed more at this time.

The valve will normally be powered by electricity – effectively, it is an electro-magnet that becomes charged and then pulls the valve one of two ways. Turn off the electrical power to the system, there should be an obvious switch somewhere, and then try turning it on again.


Step 3

If you still have no luck, your pump may be the problem. The pump is like a mini water-mill; it takes the heated water from the boiler and forces it down the flow pipe to take it to either the taps or the radiators. There could be a blockage here or the pump might not be working properly. This is also powered on electricity. So turn off the power to the pump, have a little look and see if there is any obvious sign of a problem. If it looks like a mud-pie down there, give it a good clean.

Step 4

Air can become trapped in the pump area. Look for a small nut (usually metal) which can be turned to vent excess air. When all the air is out and dirty water starts staining your jeans, stop! Turn the pump back on and see if it starts moving properly.