Summary

"Not heating up" covers a wide range of underlying faults depending on whether the oven is electric or gas, and whether it's a genuine "nothing happens" fault or a "runs but doesn't reach temperature" fault — these point to different components and need to be separated early in the diagnosis. Electric ovens heat via one or more resistive elements (bake, grill, and sometimes a third fan-assisted element) controlled by a thermostat or electronic sensor and, on most modern ovens, a control PCB. Gas ovens heat via a gas burner controlled by a thermostatic gas valve, with ignition provided by a piezo igniter, electronic spark, or in older units a standing pilot light, and a flame safety device (thermocouple or flame rectification sensor) that must detect the flame within a few seconds or the gas valve closes automatically.

The safety profile of the two fuel types is very different for who can legally carry out the repair. Any UK tradesperson competent in appliance repair and correctly isolating electrical supply can diagnose and repair an electric oven's heating fault. A gas oven's internal components — burner, injector, thermocouple, gas valve, ignition system — can only be worked on by a Gas Safe registered engineer under the Gas Safety (Installation and Use) Regulations 1998. This is a criminal offence distinction, not a best-practice one.

This article splits the diagnostic tree by fuel type at the first branch, then walks through isolation, testing and the most common component replacements for each.

Key Facts

Quick Reference Table

Diagnosed the problem? Create a repair quote in minutes with squote.

Try squote free →
Symptom Fuel type Most likely cause Fix
Nothing happens at all — no light, no fan, no click Electric No power — MCB tripped, FCU fuse blown, isolator off Check circuit and FCU fuse before opening appliance
Oven light and fan work, no heat Electric Bake element failed Test continuity; replace element
Heats on grill but not bake, or vice versa Electric The failed element's circuit only — other element still working Test and replace the specific failed element
Heats but temperature wildly inaccurate Electric Thermistor/sensor fault Replace sensor; recalibrate if adjustable
Elements glow but PCB won't sustain heat cycle Electric Control PCB fault Test PCB output; replace if confirmed
No ignition attempt, no spark/click heard Gas No power to ignition module, or gas supply isolated Check FCU/battery power for ignition; check gas isolation valve
Spark/click heard but no ignition Gas Blocked injector, no gas reaching burner, low LPG bottle Check gas supply pressure; clear injector
Ignites briefly then cuts out Gas Thermocouple/FSD not holding valve open — worn or misaligned Replace thermocouple; check flame plays directly on the tip
Burner lights but oven never reaches temperature Gas Gas thermostat valve fault, or door seal allowing heat loss Test thermostat; check door seal condition
Intermittent fault, worse when appliance is warm Either Thermal-sensitive PCB or wiring connection fault Test under load once warm; inspect connectors for heat damage

Detailed Guidance

Step 1: Establish fuel type and isolate correctly

Electric oven:

  1. Locate the dedicated circuit at the consumer unit (typically labelled "Cooker" or "Oven").
  2. Switch the MCB/RCBO to OFF, and switch off the cooker control unit/isolator.
  3. Confirm dead with a non-contact voltage tester at the appliance terminals before opening any panel.

Gas oven:

  1. If any internal component inspection or repair is needed, this is Gas Safe registered engineer work only — do not proceed as a general tradesperson beyond checking the external isolation valve and confirming the appliance is receiving gas.
  2. The engineer will isolate the gas supply at the appliance's own isolation valve and confirm the electrical supply to the ignition system is also isolated before opening the appliance.
  3. A tightness test is required after any gas-side component replacement or reconnection, per the Gas Safety (Installation and Use) Regulations 1998.

Step 2: Diagnostic tree

Oven not heating up
│
├── ELECTRIC OVEN
│     │
│     ├── No power at all (no lights, no fan, no display)
│     │       → Check FCU fuse / MCB / cooker isolator
│     │       → Power confirmed present → check internal wiring/PCB
│     │
│     ├── Power present, no heat from either element
│     │       → Test both elements for continuity
│     │       → Both open circuit → check shared supply wiring/PCB fault
│     │       → One element open circuit → replace that element
│     │
│     ├── One function heats, other doesn't
│     │       → Isolate and test the non-working element/circuit specifically
│     │       → Replace failed element
│     │
│     └── Heats but inaccurate temperature
│             → Test thermistor/sensor resistance against manufacturer spec
│             → Replace sensor if out of range
│
└── GAS OVEN (Gas Safe registered engineer required beyond this point)
      │
      ├── No ignition attempt
      │       → Check ignition module power (mains or battery-powered piezo)
      │       → Check gas isolation valve is open
      │
      ├── Spark/ignition attempt but no flame
      │       → Check gas reaching burner (pressure test)
      │       → Check/clear burner injector
      │
      ├── Flame lights then cuts out within seconds
      │       → Thermocouple/FSD fault or misalignment
      │       → Replace or realign; retest
      │
      └── Burner runs continuously but oven doesn't reach set temperature
              → Test gas thermostat valve
              → Check door seal for heat loss

Testing and replacing an electric oven element

  1. Isolate electrically and confirm dead.
  2. Remove the oven's back panel or the element's retaining screws at the rear interior wall (method varies by model — some elements hinge down for access, others require rear panel removal).
  3. Disconnect the element's wiring terminals (photograph first).
  4. Test resistance across the element terminals with a multimeter — infinite resistance (open circuit) confirms failure; compare against manufacturer spec if a reading is present but seems abnormally high.
  5. Fit the replacement element, matched by part number and wattage — never substitute a different wattage, as this changes the current draw the circuit was designed for.
  6. Reconnect wiring, refit the element and any panels, restore power, and test a full heat cycle with an oven thermometer to confirm the set temperature is actually reached.

Element replacement typically costs £25–£70 in parts and 30–60 minutes labour.

Testing and replacing a thermocouple or flame supervision device (Gas Safe engineer)

  1. Isolate gas and electrical supply, confirm dead/off.
  2. Access the burner assembly, typically via removing the oven floor plate or base panel.
  3. Check the thermocouple or FSD probe tip sits directly in the flame path — misalignment (bent probe, knocked out of position during a previous repair or cleaning) is a common cause of intermittent cutout even with a healthy component.
  4. If misalignment isn't the cause, test thermocouple output with a millivolt meter under flame (typical healthy reading in the region of 20–30mV, dropping sharply if worn) or replace as a routine service item if reading is marginal.
  5. Refit, restore gas and power, relight, and carry out a tightness test on any disturbed gas joint before leaving the appliance.

Thermocouple/FSD replacement typically costs £15–£40 in parts and 30–60 minutes labour, engineer time.

When to recommend replacement over repair

Frequently Asked Questions

Can I replace an electric oven element myself without any registration, or does it need Part P?

Like-for-like appliance component replacement (an element, a thermistor, a door seal) is not notifiable under Part P — Part P covers fixed wiring work such as new circuits or consumer unit changes, not repair of an existing appliance on its existing circuit. Any competent tradesperson can carry out this repair. If the fault investigation reveals the fixed circuit itself needs work (e.g. replacing a failing cooker control unit or upgrading undersized cable), that remedial work is notifiable.

My customer's gas oven lights but then cuts out after about 20 seconds every time — what does that point to?

A classic thermocouple or FSD symptom — the flame lights, but the safety device either isn't heating up fast enough to signal "flame present" to the gas valve, or is misaligned so it's not sitting fully in the flame. On thermocouple systems specifically, roughly 20–30 seconds is the typical window before the valve closes if the device hasn't reported a flame — check alignment first, then replace the thermocouple if alignment is correct.

Is it safe to use an oven that heats unevenly rather than not heating at all?

It's usable but should be flagged to the customer as a developing fault rather than left. Uneven heating on an electric oven often means one element (commonly the fan-assist ring element) has partially failed or the fan itself isn't circulating air correctly; on a gas oven it more often points to a burner or injector partially blocked, reducing flame spread. Neither is a safety issue in the way a gas leak or flame-out would be, but both will worsen and are worth quoting for proactively.

How do I know if the fault is the PCB rather than the element or thermostat?

Test the component itself first — if the element (electric) or thermostat/FSD (gas) tests healthy in isolation but still doesn't receive the expected signal or power during a commanded heat cycle, the fault is upstream in the PCB or wiring. Multimeter testing at the component, then working backward toward the control board, avoids unnecessarily replacing a PCB (often the most expensive single part) when the actual fault is a cheaper component.

Does a gas oven need an annual safety check even if nothing seems wrong?

Yes — landlords are legally required to have gas appliances checked annually under the Gas Safety (Installation and Use) Regulations 1998, and it's strongly recommended for owner-occupiers too. An annual service by a Gas Safe registered engineer catches early-stage burner, injector and FSD wear before it causes a "no heat" callout, and confirms the appliance is operating safely (correct flame picture, no spillage of combustion products).

Regulations & Standards