Not All Radiators Heating Up
I've fully bed all the radiators in my house multiple times and there's no trapped air. All valves are fully open but the upstairs radiators only seem to turn on occasionally and I can't understand why. Any ideas? The pressure on the boiler is unchanged and in the target range (apart from when I've bled and repressurized the boiler)
Advice from 4 local tradespeople
Likely Causes & Diagnoses:
1. Faulty or Sluggish Circulation Pump
• If the pump isn’t circulating hot water efficiently, it may struggle to push water upstairs — especially when demand is high or the system is partially sludged.
• Diagnosis Tip: Feel the pump housing. Is it hot? Is it vibrating or silent? A weak or seized pump can allow partial heating downstairs but fail to reach upstairs consistently.
2. Partially Blocked System / Sludge Build-up
• Over time, sludge (magnetite) builds up and restricts flow, especially in upstairs pipework or older systems.
• Diagnosis Tip: Check if upstairs rads take much longer to heat than downstairs — or feel cooler at the bottom. A power flush or Magnaclean install may be needed.
3. Unbalanced System
• Even if all valves are open, radiators need balancing to ensure even heat distribution — otherwise, water takes the path of least resistance (usually downstairs).
• Diagnosis Tip: Try partially closing lockshield valves on the downstairs radiators to force more flow upstairs.
4. Pump Settings or Wrong Speed
• Some newer boilers or system pumps have adjustable speeds. If set too low, they may not circulate water strongly enough to upstairs rads.
• Diagnosis Tip: Check pump speed settings (if accessible) — increase to medium or high if it’s on low.
5. Zoned Heating Valve Fault (if applicable)
• If you have a two-zone system (upstairs/downstairs), a stuck or intermittent motorised valve could be the issue.
• Diagnosis Tip: Check if your system uses motorised valves (usually near the hot water cylinder or boiler), and listen/feel if the upstairs zone valve is opening properly when demand is present.
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Recommended Next Steps:
• Start by trying system balancing (adjust lockshield valves downstairs).
• Then inspect the circulation pump for noise, heat, or signs of weakness.
• If the issue persists, consider a power flush or at least a chemical cleanse of the system.
• If zoned, test or replace the motorised valve controlling upstairs flow.
Let me know what boiler make/model you’re running or if you want a step-by-step to test the pump or balance the rads — happy to walk you through it.
Sounds like it’s poor flow first check pump is good
The radiator that are getting warm need to be isolated by the TRV or lock shield your basically allowing the boilers pump to only pump water to the rads that aren’t getting warm so say there are 5 radiators and only 3 of them are getting warm isolate the 3 that are getting warm then wait as the heat pushes its way through to the other two cold radiators.
This indicates that you system might need a power flush and a look at the magnetic filter if your system doesn’t have one, one should be installed.
Either the valve pin in the trv is stuck, or your radiators need balancing for optimal heat throughout the system
