Breakdowns & repairs
Boiler heats water but not the radiators: understanding the fault
Domestic hot water still works, but the radiators stay cold: this classic symptom often has a specific cause, from a mistakenly set summer mode to a stuck three-way valve. We explain what you can check yourself and what requires a heating engineer's intervention.
By DPS Chauffagiste · Published on 22 September 2026 · 2 min read
This article was translated from French.
A common symptom, several possible causes
You turn on the tap and hot water comes out without any trouble, but the radiators stay cold or lukewarm despite the boiler apparently running. This is one of the most frequent symptoms we come across during call-outs in Brussels, especially at the start of the heating season. The good news is that it already points to a limited number of possible causes. The less good news is that some of these causes can be fixed in two minutes, while others require dismantling and the intervention of a professional.
In a standard boiler, domestic hot water production and the radiator heating circuit share the same burner, but are directed differently depending on demand. If the hot water works, this means the boiler is properly firing its burner and heating the water correctly. The problem therefore lies further along, in the way this heat is then routed towards the heating circuit.
First step: check the operating mode
Before imagining a complex mechanical fault, it's worth checking two or three simple settings. A good proportion of the calls we receive for this symptom are actually resolved by a simple change of mode or setting.
Summer mode activated by mistake
Most modern boilers offer a
Further reading
Your boiler's safety valve keeps dripping: should you worry?
A small trickle of water under the boiler often puzzles Brussels households. We explain what the safety valve does and how to tell normal weeping from a leak that needs attention.
3 October 2026 · 7 min read
Breakdowns & repairsBoiler giving off steam or white smoke on start-up: should you worry?
A plume of white vapour escaping from your boiler's flue in cold weather is, in most cases, simply a perfectly normal condensation phenomenon. We explain how to tell it apart from the signs that should genuinely alert you.
1 October 2026 · 7 min read
Breakdowns & repairsThe Boiler Circulator Pump Sticking After Summer: An Easy Symptom to Spot in Brussels
Every autumn, Brussels homeowners switch their boiler back on and find that the radiators stay cold despite the burner running. Often, the culprit is the circulator pump, left standing still all summer. Here's how to recognise this symptom and why it deserves proper attention during servicing.
29 September 2026 · 6 min read
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