Home › Heating problems › A radiator stays cold
Heating engineer · Brussels and Wallonia
A radiator stays cold or lukewarm
A radiator that heats badly isn't always the same fault. Where it stays cold almost always gives you the answer.
The most common causes
Lukewarm at the top, hot at the bottom
There's air in the radiator: bleeding it is usually enough.
Cold at the bottom, hot at the top
Sludge has settled at the bottom. It isn't air: bleeding won't help, the system needs flushing.
Completely cold, inlet pipe hot
The thermostatic valve is often stuck: its small pin stays pressed in, especially after the summer.
Upstairs radiators heat less
The pressure is too low, or water struggles to reach the upper floors.
All radiators cold
The problem is the boiler, the pump or the thermostat: see « The boiler won't start ».
What you can check yourself
- Turn the radiator valve fully open, then check the heating is actually on.
- Lukewarm at the top or gurgling: bleed the radiator (guide below), then check the pressure.
- Completely cold: unscrew the thermostatic head (usually by hand). If the small pin underneath stays pressed in, push it gently a few times to free it, then screw the head back on.
- Only upstairs: check the pressure gauge.
Don't
- Forcing the pin with pliers or a tool.
- Bleeding with the boiler running: wait for the radiators to cool.
- Bleeding again and again a radiator that's cold at the bottom: it's sludge, not air.
Call us if…
- The radiator stays cold even after bleeding.
- It's cold at the bottom: it needs flushing.
- The valve pin won't free up.
- You have to bleed very often: air is getting into the system.
What does a repair cost?
Call-out and diagnosis: €125 excl. VAT. The repair is extra, and you get its price before we start. We usually come within 24 hours (working days) and let you know 1 hour before we arrive.
This advice applies to most boilers. Every appliance has its quirks: if in doubt, your own manual applies, and we're happy to answer on the phone.
Frequently asked questions
My radiator is cold but the pipe is hot: why?
Hot water reaches the radiator but doesn't get in: the thermostatic valve is almost always to blame. Unscrew the head and gently free the pin. If it's stuck, we'll repair it.
My radiator stays cold after bleeding: what now?
If the bottom stays cold, it's sludge: the system needs flushing. If the whole radiator stays cold, it's often the thermostatic valve. Either way, call us.
Find out more
A breakdown, a question? Get in touch.
Call us or message us on WhatsApp. Or leave your number, with a photo of the boiler if you like: we'll call you back.
