Cold storage heaters? This guide explains how they work, what the input and output controls do, why your off-peak supply might have failed, and when you need an electrician.
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Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.
The most common reason a storage heater is cold is that it did not charge overnight. Check the input (charge) dial is turned up before bedtime, then check the off-peak circuit MCB in the consumer unit. If every heater is cold but the rest of your power works, the off-peak supply — the time switch, radio teleswitch or smart meter switching — has likely failed, which needs an electrician or your energy supplier.
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Storage heaters are the primary heating system in many UK homes, particularly flats and properties without gas. When they stop working — especially in winter — it is urgent.
The good news is that storage heaters are mechanically simple. The bad news is that diagnosing faults requires understanding how they charge, how the off-peak electricity supply works, and what the controls do. This guide covers all of it.
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A storage heater is fundamentally a box of thermal bricks with electric heating elements embedded inside them. During the off-peak period (typically midnight to 7am on Economy 7), the elements heat the bricks to a high temperature. During the day, the stored heat radiates out into the room.
Storage heaters are sized to the room. The figures below are indicative of common domestic models — always confirm the actual rating from the appliance data plate before sizing the cable and protective device.
Several heaters are usually grouped on one off-peak distribution board, so the diversity and total connected load — not a single heater — determine the supply cable and main off-peak protective device.
Storage heater faults fall into two categories: problems with the heater itself and problems with the off-peak supply.
The single most common cause of a cold storage heater. If the input is at zero, no charging occurs overnight. Turn it up to 3-5 (out of 5) in cold weather before bedtime.
The circuit breaker for the off-peak supply may have tripped. Check the consumer unit — there will be a separate MCB (or pair of MCBs) for the off-peak circuits.
The off-peak supply is controlled by a time switch or radio teleswitch. If this device fails, no power reaches the heaters during the off-peak period. This requires an electrician or your energy supplier.
Elements are embedded in the thermal bricks and fail over time. A heater with one failed element out of two will still produce some heat but noticeably less. When all elements fail, the heater is dead.
The charge thermostat limits the maximum temperature of the bricks. If it fails open, the heater does not charge. If it fails closed, the heater could overheat — though a thermal cutout provides secondary protection.
Many storage heater problems are caused by misunderstanding the controls. Here is a clear explanation:
Dial numbers vary by make and model — these are general guides, not precise temperatures. The golden rule: the input only affects the next overnight charge, so turning it up in the morning does nothing for that day.
Usually a dial numbered 1 to 5 (or 1 to 6). This must be set BEFORE the off-peak period starts. In cold weather, set to 4 or 5. In mild weather, 1 or 2. Setting it to zero means no heat is stored. Changing the input during the day has no immediate effect — it only affects the next overnight charge.
A flap or damper that controls heat release. Keep it closed (or on low) in the morning and open it gradually through the day. This makes the stored heat last. Opening the output fully in the morning will release all the heat quickly, leaving you cold by the afternoon.
Some modern storage heaters have a convector boost element that uses peak-rate electricity for immediate top-up heat. This is expensive to run but useful for occasional cold snaps. It is separate from the main storage elements.
Storage heaters depend on off-peak electricity — a cheaper tariff available during designated hours. The exact window depends on your tariff and supplier, and on whether your meter runs on local clock time. Common patterns are shown below.
Off-peak rates are typically cheaper than the standard daytime rate, but the peak-rate units on these tariffs are usually dearer than a single-rate tariff — they only pay off if most of your usage is genuinely off-peak. Check your latest tariff for the exact times and prices.
The off-peak supply is typically controlled by one of these methods:
If all your storage heaters are cold but the rest of your electricity works, the off-peak supply control is the first thing to investigate.
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Use the symptom below to jump to the most likely cause before you start poking around the consumer unit.
Check that the input is turned up. In winter, set it to 4 or 5. Wait for the next overnight charge period before concluding there is a fault.
Check the off-peak circuit MCB. It may be labelled "off-peak", "storage heaters", or "Economy 7". If it has tripped, reset it once. If it trips again, stop and call an electrician — a repeatedly tripping breaker is signalling a real fault, not a nuisance.
If visible, check that the time switch clock shows the correct time. After power cuts, the clock may need resetting. Some time switches have a manual override — try it.
If some heaters work but one does not, the fault is with that individual heater (element or thermostat failure) rather than the supply.
Call an electrician if:
Storage heater work requires understanding of off-peak metering and dual-tariff installations:
Check the time switch or teleswitch for correct operation. Verify the off-peak contactor (if fitted) is engaging. Check voltage at the off-peak distribution board during the off-peak period. If the supply is controlled by a radio teleswitch and it has failed, the supplier needs to replace it.
Isolate the circuit. Disconnect the element wires. Test element resistance — should match the rated wattage (R = V squared / P). Test insulation resistance at 500V between element and earth — minimum 1 megohm. Low IR readings confirm insulation breakdown.
Modern storage heaters (Dimplex Quantum, Elnur, etc.) are significantly more efficient with fan-assisted heat release and automatic controls. When replacing, check the circuit capacity — modern high-output heaters may require a larger cable and MCB. Where the existing circuit is unaltered, a Minor Works Certificate (Reg 644.4.201) is appropriate. If the circuit cable or protective device is uprated, or a new circuit is provided, an Electrical Installation Certificate is required instead. In dwellings, the work may also be notifiable under Part P of the Building Regulations.
A free-standing storage heater is a space heating appliance, so it is covered by the protection-against-overheating requirements of Chapter 42. Regulation 424.1 of BS 7671 states that locations containing space heating appliances must comply with the appropriate parts of the Building Regulations. Apply the general Chapter 42 principles: keep adequate clearance from combustible materials, and route wiring so that the heat output does not reduce the current-carrying capacity of nearby cables. Note that Section 753 (heating cables and embedded heating systems) is scoped to embedded surface heating — floors, ceilings, walls, de-icing and the like — so it does not apply to a free-standing storage heater appliance.
Under BS 7671:2018+A4:2026, Regulation 421.1.7 requires arc fault detection devices (AFDDs) conforming to BS EN 62606 for single-phase AC final circuits supplying socket-outlets rated not exceeding 32 A in high rise residential buildings (HRRBs), houses in multiple occupation (HMOs), purpose-built student accommodation and care homes; for all other premises AFDDs are recommended on those socket-outlet circuits. Because the regulation is written around socket-outlet final circuits, it does not directly mandate an AFDD on a hardwired storage heater circuit — but the underlying fire-risk thinking is the same, so where AFDD protection is provided at the board it is sound practice to cover the off-peak heating circuits too, and to record the design decision.
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