Central Heating Glossary

Heating jargon, in plain English.

This central heating glossary explains the terms you will come across when reading about power flushing, sludge, cleaning and protection. No jargon for its own sake, just clear definitions, each linking to a fuller guide where there is one, so you can understand exactly what your engineer is talking about.

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The short answer

This central heating glossary defines the most common terms used around power flushing and system cleaning, from sludge and magnetite to inhibitor, microbore and BS 7593. Each definition is short and plain, and links to a detailed guide where we have one, so you can quickly understand any term and dig deeper if you want to.

Heating terms, explained

BS 7593

The British Standard for the treatment of water in domestic central heating systems, covering cleaning the system and adding a corrosion inhibitor. See our guide to the completion record and BS 7593.

Chemical flush

A gentler clean that circulates cleaning chemicals through the system using its own pump to remove light sludge. See chemical flush.

Corrosion inhibitor

A chemical added to the system water that slows the corrosion which creates sludge, helping protect the metal inside the system. See central heating inhibitor.

Flow and return

The two pipes connecting a radiator to the system: the flow carries hot water in, and the return carries cooler water back to the boiler.

Heat exchanger

The part of the boiler that transfers heat into the water. Limescale can build up here, while sludge and poor circulation can also contribute to overheating and kettling.

Kettling

The rumbling or whistling noise a boiler makes when limescale and sludge cause the water to overheat and boil. See boiler kettling.

MagnaCleanse

A branded rapid magnetic cleanse that captures magnetite while the system circulates, quicker but generally less thorough than a power flush. See power flush vs MagnaCleanse.

Magnetic filter

A device fitted to the system that captures circulating magnetite, helping protect a cleaned system when it is maintained properly. See magnetic filter installation.

Magnetite

A magnetic form of iron oxide and the main ingredient in heating sludge. See sludge and magnetite explained.

Microbore

Narrow central heating pipework, common in some homes, which blocks more easily with sludge and needs extra care when cleaning.

pH and TDS

Measures of the system water’s acidity (pH) and total dissolved solids (TDS), sometimes tested to judge water quality after a clean.

Power flush

A thorough clean that uses a dedicated high-flow machine to remove sludge from the system radiator by radiator. See power flushing in London.

Radiator balancing

Adjusting the radiator valves so hot water is shared evenly across the system, used when some rooms are warmer than others. See radiator balancing.

Sludge

The black, muddy build-up of magnetite that forms as a system corrodes, restricting flow and causing cold spots. See central heating sludge.

System water

The water that circulates around your central heating system, carrying heat from the boiler to the radiators and back.

Thermostatic radiator valve (TRV)

A valve on a radiator that adjusts its heat output based on room temperature, letting you set different temperatures in different rooms.

Keep reading

Still not sure what something means?

Tell us your symptoms or send a photo of the radiator water and we will explain what is going on in plain English, then confirm a clear quote for any agreed work.

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From our customers

What our customers say

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Manjinder Sanghera

Very good experience from start to finish. The appointment was easy to arrange, the engineer arrived on time and took care around the house while working. The heating is now running much better than before.

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P Miles

I contacted Power Flush London because some of my radiators were taking ages to heat up. The team explained the likely causes clearly and checked the system before recommending anything. The service felt honest and professional.

Princess Malcolm

I contacted Power Flush London because some of my radiators were slow to heat up. Simon was polite and easy to deal with, and Steve did a thorough job checking the system before starting. The whole process felt honest and professional.

Jodie-Deane Morris-Hewitson

Really good service. They did not just turn up and push a power flush. The system was checked first, the options were explained and the quote was clear before the work went ahead.

Jamie N Kent

Power Flush London were very professional. The engineer explained the issue clearly, protected the work area and carried out the job carefully. They left my home as clean and tidy as it was when they arrived. The all the radiators feels much more hotter to the touch now. Looking forward to see how it performs in the coming winter months.

Serak Henok Tesfai

I had a few radiators that were not heating properly and Power Flush London were very helpful. They checked the system first rather than just pushing the work, which I appreciated. Professional and tidy throughout.

Belle Howard

Really good service from start to finish. The booking was straightforward, the engineer arrived when expected and the work was carried out neatly. Everything was explained clearly and the heating is working much better now.

Day Walker

Power Flush London were professional from start to finish. Simon made the booking simple and Steve carried out the work carefully, checking the radiators and explaining the results. The heating is working much better and the house was left clean.