Immersion Heater Not Working? Storage Heater Faults Explained by a Rotherham Electrician

You go to run a bath and the water is barely lukewarm. Or the storage heaters felt fine first thing, but by five o’clock the living room is freezing again.

Both are calls I get week in, week out. Round Rotherham there are loads of ex council houses, flats and bungalows still running immersion and night storage heaters, and a lot of that kit is getting on.

Plenty of these faults are simple once they’re tracked down properly. Here’s how both systems work, what goes wrong, and what an electrician can (and can’t) sort.

Quick answer

If your immersion heater isn’t working, the usual culprits are a failed element, a faulty or tripped thermostat, a burnt out switch or a problem with the timer. If storage heaters aren’t holding heat, it’s often the input setting, a failed element or thermostat, or the off peak supply not coming on. A local electrician can test the circuit and parts to find which it is before anything gets replaced.

How an immersion heater works

An immersion heater is basically a big electric kettle element sat inside your hot water cylinder. There are three main parts.

The element

This is the long metal rod that screws into the cylinder and heats the water.

The thermostat

The thermostat slides into a tube alongside the element and switches it off when the water reaches the set temperature. Many modern immersion thermostats also have a safety cut out, so if the water gets far too hot it shuts off and stays off until it’s reset.

The switch and flex

The immersion should be fed from its own circuit through a 20A double pole switch, usually with a neon light that shows when power is getting through. From there a flex runs down to the immersion itself.

The top of a cylinder gets hot, so it wants a heat resistant flex. Ordinary white flex can go brittle over the years, and I see that fairly regularly in older airing cupboards.

Common immersion heater faults

No hot water at all

Start with the easy checks you can safely do yourself:

• Is the switch on and is the neon lit?
• Is the timer set correctly, and has the time drifted after a power cut?
• Has anything tripped in the consumer unit?

If the neon is lit but the water stays cold, the fault is usually in the element or thermostat. That needs testing, so please don’t go taking the cover off the immersion yourself.

Element failed

Elements wear out, especially where scale builds up on them. Testing tells us quickly whether the element is open circuit or breaking down.

Thermostat stuck or failed

A thermostat can fail so it never switches on, or less commonly so it never switches off. Scalding hot water is worth getting checked straight away.

RCD tripping when the immersion comes on

As an element ages, the outer sheath can start to leak a small amount of current to earth. That’s often enough to trip the RCD, sometimes only when the water heats up.

If your electrics trip every time the immersion kicks in, switch it off at the double pole switch and give us a call. There’s more on this in our guide, RCD, RCBO, AFDD and surge protection explained.

Scorched switch or heat damaged flex

A brown or blackened immersion switch is a sign of a loose connection or a switch that’s worn out from years of heavy use. If you can see scorching, smell burning or the switch is hot to touch, turn it off and don’t use it until it’s been checked.

Heat damaged flex is the same. Swapping it for proper heat resistant cable is a quick job.

Dual immersions and timers

Some cylinders have two elements. The bottom one heats the whole tank, usually on cheaper overnight electricity, and the top one heats a smaller amount at the top as a daytime boost.

A decent immersion timer helps too. Setting it to run during your off peak hours, if you have them, is usually the cheapest way to heat water on an electric setup. Citizens Advice has good guidance on using immersion and storage heaters efficiently.

Where the electrician’s job ends and the plumber’s begins

As electricians, we can test the circuit, the switch, the flex, the thermostat and the element itself. We can replace the switch, the flex, the timer and usually the thermostat, as it sits in a pocket and doesn’t involve opening up the water side.

Replacing the element itself is a different matter. It normally means draining the cylinder and dealing with the seal, and that’s plumbing work. In a lot of cases the sensible route is for us to confirm the element has gone and for a plumber to change it, then we reconnect and test. We’ll tell you honestly which applies.

How storage heaters work

Storage heaters are a common sight in flats and bungalows across Wickersley, Bramley, Maltby and the wider Rotherham area. They charge up overnight on cheaper electricity and let the heat out during the day.

The off peak supply

Most storage heater homes are on an off peak tariff like Economy 7. You get a lower rate for about seven hours at night, and the exact times depend on your meter and supplier.

So storage heaters normally sit on their own circuits, controlled by the meter or a timeswitch, often with a second consumer unit or separate breakers just for the heaters.

Input and output controls, in plain English

Most older storage heaters have two dials:

• Input (sometimes called charge): how much heat the heater stores overnight. Higher means more heat stored and more electricity used.
• Output (sometimes called room temperature or boost): how quickly that stored heat is let out during the day.

A common mistake is having output turned up in the morning. The heater dumps its heat early and there’s nothing left by evening. Turn output low while you’re out, then turn it up when you need the warmth.

Common storage heater faults

Not charging at all

If the heater is stone cold in the morning, check the input dial and the switch next to it first. If one heater is cold and the rest are warm, it’s often an element, thermostat or connection fault in that unit.

If every heater is cold, the issue may be with the off peak supply. A fault at the meter or its switching belongs to your energy supplier, but we can test and confirm where the power stops.

Cold by evening

Usually a settings issue, as above. It can also point to failing elements or a heater that’s simply too small for the room.

Overheating

Casing too hot to touch, a burning smell or the heater cutting out are all signs something isn’t right. A faulty input thermostat or a tripped safety cut out is common. Don’t cover a storage heater with washing, it needs air around it.

Tripping the electrics

As with immersions, an ageing element can leak to earth and trip the RCD. Damaged wiring at the connection point is another possibility, particularly on heaters that have been pulled away from the wall or knocked.

Older storage heaters and asbestos

Some very old storage heaters, generally ones made before the mid 1970s, may contain asbestos in their insulation. You can’t reliably tell by looking.

Please don’t dismantle an old storage heater to take a look inside, and don’t break one up for the tip. If you think a heater could be that old, leave it alone and get advice first. The HSE has guidance on asbestos, which it says can be found in buildings built before 2000.

Repair or replace?

Repair often makes sense when:

• The heater or immersion is in decent condition and the fault is a single part
• The switch, flex or thermostat is the problem
• The rest of the circuit tests fine

Replacement is worth thinking about when:

• The unit is very old, with several parts failing
• The casing or internal insulation is in poor shape
• Parts are no longer available

Modern high heat retention storage heaters are designed to hold their heat for longer and are worth a look if you’re replacing old units. Every job is quoted properly after we’ve had a look, and it’s free to ask.

If your wiring is getting on a bit too, an EICR on your home is a good way to see the bigger picture. Owner occupiers have no legal duty to get one, but it’s useful peace of mind. If the fuse board itself is the weak spot, have a read about our consumer unit upgrades, which come with a fire extinguisher fitted inside as standard.

Frequently asked questions

Why is my immersion heater switch light on but there’s no hot water?

The neon shows power is reaching the switch. If the water stays cold, the element or thermostat has usually failed. It needs testing by an electrician.

Can an electrician replace an immersion element?

We can test it and confirm it has failed. Changing the element normally means draining the cylinder, which is plumbing work, so a plumber often does that part and we handle the electrics.

Why does my immersion heater trip the electrics?

An ageing element can leak current to earth, which trips the RCD. Switch the immersion off at its switch and get it tested.

Why are my storage heaters cold by the evening?

Most often the output dial is set too high early in the day, so the heat is used up. Failing elements or thermostats can also be the cause.

Do old storage heaters contain asbestos?

Some very old ones can. Don’t open or dismantle an old heater yourself. Get advice first if you think it could date from before the mid 1970s.

Do you cover areas outside Rotherham?

Yes. As a local electrician we cover Rotherham and much of South Yorkshire, including Sheffield, Barnsley and Doncaster.

Related services and guides

• Electrical fault finding
• Landlord electrical services
• EICR testing in Rotherham
• RCD, RCBO, AFDD and surge protection explained
• Earthing and bonding explained

Contact MP Electrical

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