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Scarlet Heating & Plumbing

Heating & radiators

Cold rooms are usually a system problem,not a boiler problem

People replace perfectly good boilers because the back bedroom never warms up. Nine times out of ten the boiler was fine and the system around it needed flushing, balancing or resizing — at a fraction of the cost.
Power flush
From £450
Typical job
Half day to two days
Includes
Filter and inhibitor
Book a heating surveySize a radiator

Diagnose it yourself

What your radiators are trying to tell you

Put your hand on the radiator. Where it is cold tells you almost everything — and it is the difference between a bleed key and a power flush.
Common central heating symptoms, their causes and the usual fix
What you noticeWhat it usually meansWhat fixes it
Cold at the bottom, hot at the topMagnetite sludge settled in the bottom of the radiatorPower flush plus a magnetic filter and fresh inhibitor
Cold at the top, hot at the bottomTrapped air, often after the system has been drained or topped upBleed the radiators and re-pressurise — usually a five-minute job
Far radiators never get hotSystem out of balance; the near radiators take all the flowBalance the system on the lockshield valves, room by room
One radiator stone cold, others fineSeized thermostatic valve pin, or a closed lockshieldFree or replace the valve — cheap and quick
Kettling or banging from the boilerScale and sludge on the heat exchanger causing localised boilingChemical clean or power flush before it damages the exchanger
Rooms warm slowly, bills climbingUndersized radiators for the heat loss, or flow temperature set wrongRoom-by-room heat loss calculation and radiator upsizing

Radiator sizing calculator

How much heat does that room actually need?

Room dimensions, glazing, insulation and exposure. It works out the required output in BTU and watts, and suggests a radiator size — the same arithmetic an installer does on the back of a job sheet.
Room dimensions

Metres. Pace it out if you have not got a tape — it is close enough for a guide.

What sort of room?
Glazing
External walls
Insulation

Heat output needed

5,200BTU/hr

1,500 watts · 33.6m³ room

Suggested radiator

One Type 22 radiator around 600 × 1000mm

  • Figures assume a ΔT of 50°C. Run your system at a lower flow temperature for efficiency and you will need a physically larger radiator for the same output.
  • Add roughly 10% if the room has a large patio door, or if it sits above an unheated garage or passage.
  • Whole-house jobs deserve a proper room-by-room heat loss calculation. We do that free as part of any heating quote.
Get a heating quote

Power flushing

What it is, and when it is actually worth doing

Power flushing gets sold to people who do not need it, which has given it a bad name. Here is the honest version.

What is actually happening in there

Steel radiators and water make magnetite — a black iron oxide sludge. It settles in the bottom of radiators, collects in the pump and coats the boiler's heat exchanger. It is why old systems get slower, noisier and more expensive to run every year.

How a power flush works

We connect a high-flow, low-pressure pump to the system and drive cleaning chemicals through it, reversing the flow radiator by radiator to lift the deposits and carry them out. It typically takes most of a day on a normal house.

When it is worth the money

Radiators cold at the bottom, a boiler that kettles, repeated pump failures, black water when you bleed, or before fitting a new boiler onto an old system. In those cases it is money well spent.

When it is not

If your radiators just need bleeding, or the system is genuinely clean and only needs balancing, we will tell you that and charge you for the smaller job. A flush on a clean system achieves nothing.

Power flushing machine connected to a central heating system

Always finished the same way

A flush without a filter and inhibitor is half a job — the sludge simply starts forming again. Every flush we do finishes with a magnetic filter fitted on the return and the system dosed with corrosion inhibitor. We test the inhibitor level at every subsequent service, because it depletes.

While we are there: flow temperature

Most combi boilers leave the factory set at 75–80°C and are never touched again. Dropping the heating flow temperature to around 60°C lets the boiler condense properly, which is where its efficiency actually comes from. On a well-balanced system you get the same comfort for noticeably less gas. It costs nothing and we will do it while we are there.

Also on this list

The rest of the heating work we do

  • Radiator replacement

    Upgrades, relocations, designer and vertical radiators where wall space is tight, and towel rails in bathrooms.

  • System balancing

    Setting every lockshield so each radiator gets its share of the flow. Unglamorous, and it fixes more cold rooms than anything else.

  • Smart thermostats

    Hive, Nest, Tado and Honeywell supplied, fitted and actually set up properly — including the schedule.

  • Zoning and TRVs

    Splitting upstairs and downstairs onto separate zones, or smart TRVs so you stop heating empty rooms.

  • Unvented cylinders

    Mains-pressure hot water for properties where a combi cannot keep up. Installed and commissioned to G3.

  • Pumps and valves

    Circulating pumps, motorised valves, wiring centres and programmers — the parts that quietly fail and stop everything.

Straight answers

Heating questions

Mostly about cold radiators, because that is what everyone rings about.
All questions
My radiators are cold at the bottom — what does that mean?
Cold at the bottom and warm at the top usually means sludge, which is magnetite built up from internal corrosion. Cold at the top and warm at the bottom is trapped air and just needs bleeding. Sludge is treated with a power flush and prevented from returning by fitting a magnetic filter and dosing the system with inhibitor.
Why does my boiler keep losing pressure?
Losing pressure means water is leaving the sealed system somewhere. The three usual causes are a leaking radiator valve or pipe joint, a failed expansion vessel, or a passing pressure relief valve discharging outside through the small copper pipe. Topping it up repeatedly hides the problem and introduces fresh oxygenated water, which accelerates corrosion — it is worth finding the actual cause.
What size boiler do I need?
For most homes, boiler size is set by hot water demand rather than by the size of the house: roughly 24 to 27kW for a home with one bathroom, 28 to 32kW with two, and 35kW or more for larger properties with high simultaneous demand. Incoming mains flow rate matters just as much — a big combi on a weak supply performs badly. We measure the flow rate on site before recommending anything.
Do you charge for a quotation?
No. Quotes for installations, bathrooms and heating work are free, and we give you a written fixed price rather than a rough figure over the phone. Diagnostic visits for a fault are chargeable, because that is engineering time on site — but the call-out is credited against the repair if you go ahead with it.

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Get every room warm again

We will diagnose what is actually wrong before recommending anything. Ring 07490 623966 or book a survey online.

Book a heating survey07490 623966
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