Q&A - Most Important Questions about Radiators Answered

Table Of Contents:

• How to bleed a radiator?

  
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• How to remove a radiator?

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• How to paint a radiator?

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• How to bleed a radiator without a key?

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• What size radiator do I need?

  
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• How to paint behind a radiator?

  
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• Do radiator covers block heat?

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• How to clean the radiator?

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• How to turn a radiator off?

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• Do radiator covers stop heat?

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• Why is my radiator cold at the bottom?

  
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• How to turn the radiator on?

  
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How to bleed a radiator?

Radiator bleeding is one of those really easy DIY jobs which can help make your whole heating system work better. Usually, when the top of a radiator feels cold while the bottom enjoys a nice warm feeling or hears odd gurgling noises, it usually indicates that air is entrapped inside. Here's a clear step-by-step guide to follow: 

What You Will Be Needing:

• A radiator key (or a flat-head screwdriver for some modern valves) 

• An old towel or cloth 

• A small container to catch dripping 

• Optional parts: gloves to avoid splashes of hot water 

Step by Step Instructions:

1. Turn off heating: Allow radiators to cool so you are not causing burns. 

2. Find the bleed valve: It's usually at the top corner of the radiator. 

3. Insert key into the radiator: Then, slowly turn it anti-clockwise and listen for a hissing sound. This sounds when trapped air escapes. 

4. Catch any drips: The moment water flows steadily from the valve, it is in 'air-free' condition. 

5. Tighten the valve: Turn key clockwise until snug (but do not overtighten). 

6. Check boiler pressure: The bleeding can cause a drop in pressure in the system. If it is below 1 bar, top it with a filling loop. 

7. Put heating back on-check heating evenly heats from the top to bottom. 

Pro Tips:

• Start with the radiator furthest from the boiler. 

• Opening the bleeder repeatedly might indicate a bigger problem, like a leak or corrosion. 

• A low boiler pressure after bleeding can affect how your heating works. 

Bleeding Radiators Checklist 

Tools Needed:

• Radiator Key (or Flat-head Screwdriver for Some Valves) 

• Small Container or Cup 

• Old Towel/Cloth Gloves (Optional) 

Step-by-Step procedure:

• Turn Off Heating: Let the radiator cool a little. 

• Start from the radiator furnace to the end of the house. 

• Locate bleed valve: at the top corner of your radiator. 

• Insert key & turn anti-clockwise slowly. 

• Listen for the hissing sound of air. 

• Hold the container under the valve to catch drips. 

• Wait until water flows steadily (no more air). 

• Close valve-turn clockwise until snug. 

• Repeat for each radiator, moving closer to the boiler. 

• Check boiler pressure-top it up if below 1 bar. 

• Reheat the whole thing-ensure the radiator heats evenly. 

Pro Tip:

• Always work in order: furthest → nearest radiator. 

• Do not overtighten the valve. If you are continuously bleeding the radiators, it probably indicates an internal issue associated with a leak, corrosion, or faulty pump.

How to remove a radiator?

Removing a radiator is a fairly simple DIY task—whether you’re taking it off to plaster, move, or replace it—but it can get rather wet and valve‑heavy, so you need to be careful with what you’re doing.Here is a clear step-by-step guide on doing it:

Tools you’ll require:

• Radiator bleed key

• Adjustable spanner or wrench

• Bowl or bucket to catch water

• Towels or dust sheets to protect flooring

• Water pump pliers (optional, for stubborn fittings)

Step-by-Step Process:

1. Switch off the heating system: The boiler and heater must all be off completely and the radiator cool to the touch before starting.

2. Isolate the radiator: Both the thermostatic radiator valve (TRV) and the manual valve close by twisting clockwise.

3. On the other side is the lockshield valve: remove the plastic cap and twist clockwise using a spanner.

4. Count the turns of the lockshield for easy resetting afterward.

5. Bleed the radiator: Use the bleed key at the top to release air trapped inside the radiator and check that it has been isolated. There may be a bit of water escaping while bleeding from the radiator.

6. Drain the radiator: Place an under-one-valve bowl, slowly loosening the nut connecting it to the radiator. Some water will then start to flow out; try to catch as much as possible in the bowl. Once drained, repeat on the other side.

7. Disconnect and clear off: When both valves fail to connect, lift off the radiator very carefully from its wall brackets. Tilt it a little to allow any residual water to drain into your bowl.

8. Capping or protection to pipes (if required): You might need to cap the pipes when permanently removing the radiator. Otherwise, temporarily removing it (for painting), leaving the valves closed will work. 

Safety note: When taking off a radiator, it will be heavy and messy, make sure all flooring is covered and there are lots of towels available. It is really the safest way to get a professional if you are unsure about capping pipes or messing with central heating pressure.

How to paint a radiator?

Painting a radiator can give a space a new look without replacing the entire radiator. This will be a fairly easy task if the right paint is prepared and applied. A very basic step-by-step guide showing the procedure is given below:

What you require:

• Radiator paint (heat resistant, normally either an enamel or specialized radiator paint)

• Primer (if required by your paint)

• Sandpaper (120 to 240 grit)

• A damp cloth and mild detergent

• Masking tape and dust sheets

• A synthetic paintbrush or a small roller

• Optional: spray paint to give that smoother finish

Let's get started:

• Turn off and cool the radiator: Before beginning this task, make sure the radiator is absolutely cold and that the heating is off.

• Clean completely: To get rid of dust, oil, and filth, wipe down with warm, soapy water. Wash away and dry very thoroughly.

• Sand-Sand very lightly so as to remove any flaking paint and provide a key for the new paint. 

• Wipe off the dust.

• Protect surrounding areas-Mask off any valves, vents, and walls. Also, lay a dust sheet onto the floor.

• Prime (if required)-If you have a bare or rusty radiator, use a metal primer first. 

• The first coat- Spray, brush, or roller. Paint applied in thin coats, even pressure ending with brushing vertically. 

• Allow to dry completely: Stick to the paint manufacturer dry times. Usually, between coats, 6-24 hours are allocated. 

• Apply Second Coat-Make strong and smooth finish. 

• Let it Cure-Wait at least 24 hours before turning the radiator back to the ON position so that the paint properly hardens. 

Pro Tip: Always use paint meant for radiators or metal surfaces. Ordinary wall paint will discolor and begin to peel upon exposure to heat

How to bleed a radiator without a key?

Sometimes all it takes for a radiator to do its job, in fact, is bleeding it—quite a few modern radiators lend themselves to this with the use of living-room gadgets. The trick is knowing what can be used and how. Here is a plain guide to these:

Items that can be used instead a key:

• Flathead screwdriver – Many bleed valves have a slotted head that fits a standard screwdriver.

• Coin (like a large flat coin) – On some radiators, especially older ones, a coin can slot neatly into the valve.

• Some universal tools made specifically for this function – Tools like these are sold in DIY. If you want a reusable option, you can buy these.

• Avoid using pliers or cross-head screwdrivers, as they can damage the valve and cause leaking.

How to Do It in Steps:

• Turn the heating off and wait till the system cools. 

• Protect the area: Underneath the valve, put a towel and bowl.

• Insert your tool: Use a flathead screwdriver or coin in the bleed valve slot.

• Turn anticlockwise slowly. You will hear a hissing sound caused by the trapped air escaping.

• Wait for water: When you see water streaming out, and not air, close the valve by turning clockwise.

• Check the boiler pressure: Bleeding can cause a drop in system pressure, so top it up if required.

Pro tip: An actual radiator key with its cheap offer is good for the purpose of bleeding jobs over and over since it averts damage to valves and makes the business neater.

What size radiator do I need?

Great question—One of the most important considerations in choosing the correct radiator size is to assess how much heat output is required in relation to the needs of that specific room. If too small, the room will never really feel warm; if too large, wasting energy and money would be inevitable. Here’s how to work it out:

Key Factors That Decide Radiator Size

• Room dimensions – Measure length × width × height to get the cubic volume.

• Room type – Living rooms and kitchens need more heat than bedrooms.

• Windows & insulation – Large windows, poor glazing, or thin walls increase heat loss.

• Location – North‑facing rooms or those with external walls need more output.

• Desired temperature – Bathrooms and lounges are usually kept warmer than hallways.

Quick Rule of Thumb (BTU / kW)

Radiator output is measured in BTUs (British Thermal Units) or kW (kilowatts).

• Bedrooms: Multiply cubic volume × 4 (gives BTUs needed).

• Living rooms/dining rooms: Cubic volume × 5.

• Kitchens/hallways: Cubic volume × 3.

Example: A lounge 4m × 3m × 2.5m = 30m³. 30 × 5 = 150 BTUs per m³ → ~4,500 BTUs (≈1.3 kW) radiator required.

For accuracy, most people use an online BTU calculator which factors in insulation, windows, and external walls

 Pro Tips

• Always round up rather than down—better to have a slightly oversized radiator than an underpowered one.

• In large rooms, two smaller radiators often heat more evenly than one big one.

• Check your boiler capacity if you’re adding multiple new radiators.

Bedroom radiator sizing

Information needed

• Room size: Length, width, and height of your bedroom.

• Windows: Type: single, double, or triple glazing. Area: approximate size of the window(s).

• External walls: Count: how many walls face outside.

• Floor and ceiling: Below: another heated room, unheated space, or outside? Above: another heated room, loft, or outside?

• Insulation level: Quality: poor, average, or good.

• Desired temperature: Target: typical bedrooms are kept a bit cooler than living rooms.

Quick estimate method

• Rule of thumb (bedrooms): Use a range of BTU per cubic meter and adjust for your room’s losses.

BTU required≈Room volume (m3)×45 to 60

• Convert BTU to kW (if needed):

kW=BTU/3412

• Adjustments:

• Single glazing: add 10–20%.

• Two+ external walls or north-facing: add 10–15%.

• Good insulation/double glazing: subtract ~10%.

Example calculation

• Room: 4.0 m × 3.0 m × 2.6 m → volume 4×3×2.6=31.2 cubic m

• Baseline (average bedroom):

31.2×50≈1560 BTU(≈0.46 kW)

• With single glazing and two external walls (+25%):

1560×1.25≈1950 BTU(≈0.57 kW)

Choose a radiator (or pair of radiators) with a combined output slightly above the final BTU to avoid underheating.

Practical tips

• Oversize slightly: Pick the next size up; you can always turn it down.

• Distribute heat: Large bedrooms often heat more evenly with two smaller radiators.

• Check ratings: Radiator BTU outputs are listed at a specific ΔT rating; ensure you compare like-for-like when shopping.

How to paint behind a radiator?

It's jobs like painting behind radiators that feel how on earth can I reach that, but with tools and a technique, you can have a clean professional finish without removing the radiator. Here is a simple-to-understand guide that shows you exactly how it is done.

Tools you will require

• Radiator roller or mini-roller on a long handle

• Angled radiator brush (preferably use narrow bent-neck brushes)

• Dust sheets and masking tapes

• Paint tray, with suitable wall paint

• Optional: radiator removal kit if you want to take it off completely

Step-by-step guide

• Turn off and cool the radiator: Never paint beside a hot radiator-the paint will dry unevenly, and fumes could be far stronger. 

• Area preparation: Dust sheets down, mask off valves, and skirting, and clean behind the radiator using a duster or vacuum. 

• Cut with a brush: Use the angled radiator brush to paint around brackets, edges, and tight corners.

• Use a radiator roller: A slim, long-handled roller lets you reach down the back of the radiator. 

• It should be lightly loaded to avoid drips. 

• Work in sections: Paint vertically behind the radiator, then blend into the surrounding wall for a seamless finish. 

• Apply an additional coat: Once dry, repeat with no dry patches. 

Pro Tip: Thus, if you were redecorating an entire room and wanted to get a really perfect finish, you would find it much easier to temporarily remove the radiator from the wall. However, for most jobs, a radiator roller and angled brush result in finishes that look pretty much the same when finished.

Do radiator covers block heat?

The most popular method of disguising bulky radiators while providing some decorative appeal is to put on a radiator cover. The real question is whether it affects heating efficiency negatively. The short answer is yes, they can block some of the heat, but just how much depends entirely on their design.

Effects of Radiator Covers on Heat

• Radiators are convective heaters: warm air comes off from the radiator; while cooler air comes in at the bottom. 

• A solid cover with no ventilation will only trap the heat and, as such, cause the radiator to work much harder with the room taking longer to warm up. Radiator covers properly designed with slats or grilles or gaps allow the air to circulate fairly well, thereby minimizing any heat loss. Experts recommend at least a 5 cm clearance above and to the sides, and a 3 cm depth gap between the radiator and cover.

• An added benefit: covers may act as a shelf and reduce surface temperature (safer for kids) whilst absorbing noise. 

Best Practices

• Choose covers with plenty of ventilation slots.

• Avoid putting any objects directly on top that block airflow.

• In case the room feels cooler after the cover is mounted, a slightly larger radiator or removal of the cover during the winter should be considered. 

All in all, covers do block some heat, but with the appropriate ventilation design, the heat loss is minimal. Think of them as a compromise between style and efficiency!

How to clean the radiator?

Cleaning a radiator in the household may not be a great assignment, but it does great things because it boosts efficiency of heating, reduces dust in the air, and even reduces the energy bills. Here's a clean, stepwise guide to show precisely how one does it.

Tools you will require

• Attachment of vacuum cleaner brush

• Radiator cleaning brush or the long duster 

• Damp microfiber cloth

• Mild detergent or soapy water

• Towels or dust sheets

Step-by-Step Guide

• Switch off heating Allow the radiator to cool completely before cleaning.

• Vacuum the outside Use the brush attachment for sucking up dust from the top grill, sides, and around the valves.

• Clean inside fins

• Insert in the top grill radiator brush or long duster.

• Make the dust and cobwebs fall down onto a towel or sheet beneath.

• Vacuum up the debris.

• Wipe surface Use the damp cloth with mild detergent on the outside. Don't soak the radiator; too much water may cause rust.

• Detail the hard-to-reach places with a small brush for corners and brackets, even cotton swab. 

• Deep cleaning if needed If the radiator is really nasty on the inside, take off and flush with clean water outdoors (this is advanced but brings the radiator back to efficiency). 

Suggestion: 

Clean up the radiators at least once before winter. Dust insulates, meaning a radiator can lose efficiency by up to 25% at worst.

How to turn a radiator off?

Turning off a radiator is easy once you identify the kind of valve that follows it. The technique varies for both thermostatic valve and manual or lockshield valve. Here is a neat explanation of the entire process.

The Step-By-Step Guide

1. Thermostatic Radiator Valve (TRV)

• Found in most modern radiators.

• It has a numbered dial (0–5).

• To turn it off: Rotate the dial clockwise to the 0 position or off symbol.

• Some TRVs may have a frost setting, which keeps the radiator off unless the room temperature falls below ~5°C.

2. Manual Valve

• Looks like a simple round knob with no numbers.

• To turn it off: Turn clockwise until it stops.

• If stiff, steady pressure can be applied, or pliers can be used (but don’t force it).

3. Lockshield Valve

• Usually on the opposite side of the radiator, hidden beneath a plastic cap.

• Controls balance of water flow in the system.

• To fully isolate the radiator: Remove the cap and turn the small spindle clockwise with a spanner or pliers until it stops.

• Note: Count how many turns so that you can put it back to the original position later when turning on the radiator.

A pro tip: If you want to stop heat in just one room, just close the TRV or the manual value, and that is good enough. If you are removing or working on the radiator, close both valves to completely isolate it.

Do radiator covers stop heat?

Yes, indeed, radiator covers don't actually stop heat but help minimize its effectiveness in heating the room. This is contingent upon the kind of design the cover is in addition to the extent of ventilation it affords.

How Covers are Affecting the Heating of Radiators

• Convective Heat: The main way radiators heat space is by accepting cool air from below, then emitting warm air overhead. A solid cover can block this airflow, slowing circulation.

• Radiative Heat: In addition, radiators heat a space with infrared radiation. Covers act as barriers and therefore block direct radiant heat from reaching you.

• Design count: Designs with Slovenia's cover slats, grilles, or gaps at the top and sides allow warm air to exit, so heat loss minimization is not a big deal. Solid, unventilated covers are said to cut efficiency anywhere from 10 to 25 percent.

• Additional Benefits: Covers can safely secure radiators from children, minimize dust accumulation and serve as decor accents.

Bottom Line

• Surely the covers reduce heat to small degrees, but a well-ventilated design keeps the effects trivial. 

• If you're looking for aesthetics or safety, then opt for a slat or grill cover. 

• If the top priority is heat efficiency, then the radiator should remain open to avoid passing heat through the cover.

Why is my radiator cold at the bottom?

Typically, a radiator that is hotter at the top than at the bottom is indicative of something obstructing hot water flow inside. The most common offender is sludge build-up, a combination of rust, dirt, and limescale settling at the bottom over time. However, there are a few other options. Let's evaluate it closer:

Main Causes

- Sludge and debris – the number one reason. Sludge settles at the bottom where it blocks hot water from circulating.

- Trapped air in the system – usually makes the top cold but sometimes uneven circulation leads to cold patches lower down.

- Poor system balance – imbalanced radiators allow some to hog hot water while others remain cooler.

- Faulty valves or pump issues – it is rare but flow can be interfered with by a stuck thermostatic radiator valve (TRV) or weak pump.

Fixes

- Bleeding the radiator – to release trapped air (though this usually solves the cold at the top not the bottom).

- Flushing the radiator – to drain out the sludge and flush through with clean water.

- Power-flushing the system – a professional high-pressure clean for multiple radiator issues. 

- Adding an inhibitor – to prevent sludge from building up again.

- Checking valves and balancing – to have all radiators heat evenly by adjusting lockshield valves.

Pro tip: If only one radiator is cold at the bottom, it's usually sludge in that unit, and if several are affected, that means your whole system might need a flush.

How to turn the radiator on?

Turning a radiator on is usually straightforward once you know which type of valve or control you’re dealing with. Here’s a clear guide that shows you exactly how it’s done.

Step‑by‑Step: Turning a Radiator On

1. Check your heating system

• Make sure your boiler or central heating is switched on.

• If you have a room thermostat, set it to your desired temperature (usually 18–21°C for comfort).

2. Locate the radiator valve

• Thermostatic Radiator Valve (TRV): A numbered dial (0–5) on one side of the radiator.

• Manual Valve: A simple knob without numbers.

3. Turn the valve

• Rotate counter‑clockwise to open.

• On a TRV, set it to the number you want (higher = warmer).

• On a manual valve, just open it fully.

4. Check the opposite side (lockshield valve)

• Normally left as‑is, but if it’s fully closed, open it slightly with a spanner.

• This allows water to flow through.

5. Wait for heat

• The radiator should begin to warm from the bottom up within 10–20 minutes.

6. Troubleshooting

• If it stays cold, it may need bleeding (to release trapped air) or balancing.

• If multiple radiators don’t heat, check your boiler pressure or system timer.

Pro tip: If you’re just turning one radiator on in a room, remember the rest of your system needs to be running too—radiators don’t work in isolation.