Posted on: 15 October 2025
When you switch on your heating and realise one (or more) radiators are staying stone cold, it can quickly turn from a minor annoyance to a full-blown winter crisis – especially when the local temperatures here in Belfast or beyond start to dip.
Before you start piling on jumpers or threatening your boiler with violence (we’ve all been there), it’s worth checking a few simple things first. Here’s what might be going on, and when to call in the pros.
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One radiator not heating up?
If the rest of your radiators are warm but one’s refusing to play ball, there are a few usual suspects.
Trapped air
If the radiator is warm at the bottom and cold at the top, trapped air is probably the cause. Bleeding the radiator with a bleed key can release that air pocket and get things flowing again. Just make sure your heating is switched off first, and keep a cloth handy for any escaping water.
(Tip: if you’re not sure how to bleed a radiator safely, we’ve covered it in our how to guide – or call us and we’ll take care of it for you.)
Sludge build-up
If it’s cold at the bottom and warm at the top, sludge may be to blame. Over time, rust and debris can settle at the base of your radiator, blocking the hot water. We can add inhibitor to your system if it’s low or a professional powerflush will clear out that gunk and help your system run more efficiently.
Sticky TRV (thermostatic radiator valve)
Sometimes, the pin inside the TRV gets stuck, stopping water from entering the radiator. Gently freeing the pin might help, but be cautious – using too much force could make things worse. If in doubt, it’s one for solv.
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None of your radiators heating up?
If all your radiators are cold, the issue likely lies with your central heating system or boiler.
Low boiler pressure
Check your boiler’s pressure gauge. If it’s sitting below 1 bar, you’ll need to top it up. There should be instructions in your boiler manual (or on the boiler panel) or you can watch our how to guide. If pressure keeps dropping, that points to a bigger issue – time to call solv.
Boiler fault or error code
A flashing error code or extinguished pilot light means your boiler isn’t happy. Try resetting it following your manufacturer’s guide, but if the problem persists, get a Gas Safe engineer from solv to investigate.
Faulty diverter valve
If your hot water’s working but the radiators aren’t, the diverter valve inside your boiler could be stuck. This is definitely a job for a qualified Gas Safe engineer from solv – don’t try to fix it yourself.
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When to call a professional
Visual checks are fine — but never remove your boiler cover or attempt internal repairs yourself. It’s illegal to do so unless you’re Gas Safe registered, and it will void your warranty.
If you’ve checked the basics and your radiator still isn’t heating, it’s time to call in the experts. At solv, our Gas Safe and OFTEC engineers can diagnose and repair radiator and boiler issues quickly — so you can get back to a warm, comfortable home without the stress (or the guesswork).
Need a hand?
If your radiators are playing up or your heating just isn’t performing like it used to, book a repair with solv today.
✅ Fast, local service across Belfast and beyond
✅ Gas Safe and OFTEC registered engineers
✅ Clear, upfront pricing — no hidden costs
Book your boiler or radiator repair and stay warm this winter.