Guide · Home care

Boiler and Radiator Care

A plain, friendly guide for homes with hot water radiators or baseboard heat: spotting trapped air, how bleeding a radiator works, reading the pressure gauge, and what to report.

Start the checklist

Where to start

A radiator is hot at the bottom and cold at the top?
That is usually trapped air. See how to tell.
Water on the floor near the boiler?
Take a photo and tell your owner right away. See what to report.
Your owner says bleeding is fine?
Follow the steps slowly and carefully.

The short version

A boiler heats water and sends it through pipes to radiators or baseboard units. Over time, a little air separates from the water and collects at the high points. A radiator can stay cold at the top, and pipes can gurgle and slosh.

Letting that air out is called bleeding. It is a small job, but the water is hot and under pressure. In a rental, ask your owner first. Many are happy to show you, or to do it themselves.

The boiler has a gauge that shows pressure in PSI. As a general guide, in many homes it reads about 12 to 15 when cold, and a bit higher when hot. The right number varies from home to home, so ask your owner what is normal for yours. On many home boilers, a safety valve opens near 30 and can let water out onto the floor. Readings that seem low or high are worth reporting.

Expansion tanks, water feed valves and the boiler itself belong to the owner or a heating pro.

Who does what

Every home and lease is a little different, so these are examples. When you are not sure, ask first.

Residents can often

Feeling radiators for cold spots and listening for gurgling
Reading the pressure gauge and noting it
Bleeding radiators only with your owner's okay
Reporting water near the boiler or a gauge that seems off

Leave to the owner or a pro

The boiler, its pressure and its water feed valve
Checking or replacing the expansion tank
Any leak, drip or valve that will not close

How to tell a radiator has air in it

Turn the thermostat up and let the heat run for about 15 minutes.
Carefully feel each radiator or baseboard unit from bottom to top. They can be hot, so use a light touch.
Hot at the bottom or near the pipe, but cool across the top or far end? Air is trapped inside.
Gurgling or sloshing in the pipes is another sign.

If your owner says bleeding is fine

Turn the thermostat down so the pump stops, and wait until the radiators cool.
Find the small valve near the top, at one end of the radiator.
Hold a dry rag or a small cup right under it.
With a radiator key or the screwdriver your valve takes, turn it slowly counterclockwise, only until you hear air hiss. Never unscrew it all the way.
You will hear a hiss as air escapes. When the hissing stops and a steady trickle of water comes out, turn it clockwise to close it, snug but not too tight.
Wipe it dry and check for drips. Start on the lowest floor and finish on the top floor.
Let your owner know which radiators had air, since they may want to check the boiler pressure.

Try it

Your radiator checklist

From the guide’s own checklist. Tick each one as you go. These are examples; your home may need others.

0 of 6

Each radiator feels warm from bottom to top
Cold tops reported, or bled with your owner's okay
Heat turned down and radiators cooled before any bleeding
Every bled valve closed snug, dry and not dripping
Boiler pressure gauge read and noted
Any water near the boiler reported right away

What to report

Water on the floor near the boiler.
A gauge that reads very low, or close to 30.
A bleed valve that keeps dripping or will not close.
Radiators upstairs that stay cold even after bleeding.
Take a photo of the gauge and anything else you notice, and message your owner.

A quick photo and a note is all it takes. Your owner will know what to check next.

Test yourself

How much do you remember?

4 quick questions from this guide, with a one line why for each. Totally optional, no sign in, and your answers are never saved.

From The Perfect Series

Go deeper with The Perfect Seasonal Home Care Checklist Workbook

Fall, spring and everything in between. Simple, step by step checklists you can write in, one topic at a time, to help any home stay warm, safe and dry all year.

See The Perfect Seasonal Home Care Checklist Workbook All books in The Perfect Series

Keep this guide handy

Save this page, come back to your checklist any time, and share it with anyone in your home who could use it.

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From the Bunklow shop

Take it with you

Bunklow Home Guide 015: Hydronic Baseboard and Cast-Iron Radiator Bleeding and Pressure MonitoringA printable guide to hydronic baseboard and cast-iron radiator bleeding and pressure monitoring, in plain steps.
See it in the shop

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This guide shares general information to help you, and is not legal, tax or safety code advice. Rules vary by state and city, so check with your local officials or a qualified professional. Please follow the maker's instructions for your equipment. Bunklow does not inspect properties or make repairs.