An incredibly common issue people have with their central heating are radiators that will not heat up evenly, at all, or suffer from “cold spots”.

If in this situation, the first step is to bleed your radiators to release any excess air within the system that may be preventing the hot water from circulating evenly.

Bleeding the radiators is a very quick and easy task that usually resolves the issue.

But sometimes it is not so straight forward. So, what should you do if your radiator is still cold after bleeding it?

Is there a problem with your thermostatic radiator valves?

It is worth checking your thermostatic valves in case a pin is jammed, preventing an adequate amount of heating water from getting into the cold radiator.

How do you do this?

thermostat for radiator

Simply remove the cap/head on the TRV – this is the part that has the temperature numbers imprinted.

Beneath the head, you should be able to clearly see the TRV pin. Sometimes the pins can become jammed and unable to move, preventing water flow.

To unjam the pin, grip it using an adjustable spanner and attempt to move it. Wiggling the pin should loosen it and provide some slack, allowing water to flow into the radiator once more.

If your radiators start to get hot again, you know that this was the root of the problem.

Get your central heating system flushed

With time, it is normal for dirt, rust, and other deposits to build up within your central heating water, which can have a negative impact on its quality, resulting in a thick black substance known as sludge.

Sludge can cause blockages in your system, lead to corrosion, and prevent hot water from evenly circulating throughout your radiators and pipes. This can lead to cold spots and damage to your system.

In order to maintain your central heating system’s water quality and ensure your radiators remain evenly heated, carrying out a flush is recommended every 5 years.

There are a few different types of flush – a chemical flush, a power flush, and a magnacleanse. Essentially, they all work using high pressure and a combination of cleaning chemicals.

This is not really a DIY task; it is a dirty job and since dislodging sludge and deposits can expose leaks it is advised that you have a plumber present to deal with any repairs that may result.

Do you need to balance your radiators?

If a particular radiator still remains cold even after taking the above steps, it could mean that the water within your system is not being evenly distributed between all of your radiators.

This might mean that your radiators need balancing i.e. to make water flow evenly from your boiler to each radiator within your home.

For example, if the radiator furthest away from your boiler is the one that is failing to heat up, it is a pretty good sign that your system needs balancing.

Does your thermostatic radiator valve need to be replaced?   

You may want to consider replacing your thermostatic valve entirely if your radiators still remain cold.

As detailed earlier, the pin within the thermostatic radiator valves can become stuck, preventing water flow, which is usually easy to fix with a quick tinker to loosen it up.  

Yet, it is also important to realize that thermostatic valves are prone to wear and tear and over time may become dysfunctional.

In this situation, the best next step is to replace your radiator valve completely. Adding a new, functional valve will likely have your radiators getting back to heating your home efficiently in no time at all.

Annual servicing & maintenance

radiator maintenance

If none of these steps resolves your cold radiator problem, then the next best thing to do is to seek the expertise of a professional, registered Gas Safe Engineer, as you may need a new boiler replacement. They will be able to analyze every part of your system, diagnose the cause of the issue, and resolve it.

Regardless, it’s important to get your central heating system serviced once a year, not only is this usually a condition of keeping your boiler warranty valid, but it’s also a great way to spot minor issues before they spiral into a major and expensive repair.

Add chemical inhibitors

With time, various deposits can build up within your central heating system (including your radiators), including dirt, rust, and sludge. If left to fester, these deposits can result in corrosion of major components, resulting in leaks and damage that results in significant repair work.

Not only that, but sludge can collect within your radiators, causing blockages and making your systems pump work even harder to circulate the heating water.

Rust inhibitors can help prevent corrosion, so are definitely worth adding to your system and topping up periodically.

Bleeding radiators: What you need to consider? was last modified: September 28th, 2021 by Billy Guteng
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