Winter warm-up: radiators and boilers

The questions

1. Question 1 of 7Your radiator is cold at the top and warm at the bottom. What is going on?

   

   • Sludge
   • Trapped air: bleed it
   • The thermostat is broken
   • The boiler is too hot

   Show answer

   Answer: Trapped air: bleed it

   Cold at the top and warm at the bottom means air is trapped. Bleed it (Worcester Bosch). Gurgling noises are another sign (Viessmann).

   Source: Worcester Bosch: How to bleed a radiator; Viessmann: Heizung entlüften (German)

   How to bleed a radiator

2. Question 2 of 7And the opposite: warm at the top, cold at the bottom?

   • Air again, bleed it twice
   • More likely sludge: bleeding won't fix it
   • Normal in winter
   • Too much pressure

   Show answer

   Answer: More likely sludge: bleeding won't fix it

   Warm at the top and cold at the bottom is more likely sludge than air. Worcester Bosch says bleeding won't fix it and the system may need cleaning.

   Source: Worcester Bosch: How to bleed a radiator

   How to bleed a radiator

3. Question 3 of 7Which way do you turn the radiator key to let the air out?

   

   • Clockwise
   • Anticlockwise, slowly
   • Pull it straight out
   • It doesn't matter

   Show answer

   Answer: Anticlockwise, slowly

   Turn the key slowly anticlockwise until air hisses out, and close it clockwise as soon as water comes out (Worcester Bosch, Viessmann). The water can be hot.

   Source: Worcester Bosch: How to bleed a radiator; Viessmann: Heizung entlüften (German)

   How to bleed a radiator

4. Question 4 of 7In Germany, Viessmann says to start with which radiator?

   • The one nearest the boiler
   • The highest one, where most air collects
   • The smallest one
   • The bathroom towel rail

   Show answer

   Answer: The highest one, where most air collects

   Viessmann says to start at the highest radiator, where most air collects, with the pump off and all thermostats fully open for 30 to 60 minutes first.

   Source: Viessmann: Heizung entlüften (German)

   How to bleed a radiator

5. Question 5 of 7All radiators are bled. What should you check next?

   

   • The fuse box
   • The boiler pressure gauge: bleeding lets water out
   • The gas meter
   • Nothing

   Show answer

   Answer: The boiler pressure gauge: bleeding lets water out

   Every time you bleed a radiator a little water leaves the system, so the pressure falls (Viessmann). Worcester Bosch says to top it up after bleeding.

   Source: Viessmann: Heizungswasser nachfüllen (German); Worcester Bosch: Maintaining your boiler pressure (homeowner guide, PDF)

   How to top up your boiler pressure

6. Question 6 of 7Worcester Bosch's homeowner guide: top up to what reading, with the heating cool?

   • 0.2 to 0.5 bar
   • 1 to 1.5 bar
   • 3 to 4 bar
   • As high as it goes

   Show answer

   Answer: 1 to 1.5 bar

   Worcester Bosch gives 1 to 1.5 bar, read with the heating cool because the reading rises while it runs. Other makes may use a different range, so check your boiler's manual.

   Source: Worcester Bosch: Maintaining your boiler pressure (homeowner guide, PDF)

   How to top up your boiler pressure

7. Question 7 of 7The pressure keeps dropping and you haven't bled anything. Best move?

   • Top it up every morning
   • Call a heating engineer: a leak or the expansion vessel is likely
   • Turn the heating off until spring
   • Bleed more radiators

   Show answer

   Answer: Call a heating engineer: a leak or the expansion vessel is likely

   Viessmann names a leak or a faulty expansion vessel as the most common causes. That is a job for a heating engineer, not a top-up.

   Source: Viessmann: Heizungswasser nachfüllen (German)

   How to top up your boiler pressure