The diagram below shows how a central heating system in a house works.
Sample Response
The given picture illustrates how a central heating system operates in a typical house in order to keep internal climate and tap water at a pre-set temperature. The process runs through two stages, starting at a transitory state until reaching a steady state.
In the transitory stage, the main goal is to fill the heater´s piping circuit up with water. Initially, cold water is taken from the local water utility supplier and passed through a boiler, which is a device designed to exchange energy between burned fuel (gas or oil) and water, this fluid is then pumped through some tubes and radiators, which are equipment used for exchanging temperature between the running fluid and the air inside the house. Finally, water reaches back to the boiler. The amount of water taken from the utility service has a specific volume according to an engineering design, this stage continually repeats until the water gets a predefined temperature.
Once the system has reached the pre-set temperature, that is when it gets to steady state, thanks to the high pressure on the piping circuit, water is transported to a storage tank from the boiler, after the storage tank is completed, water runs down to a sink and when the pressure again is high enough, water deviates towards a spare water tank which functions as a water reserve for when the service is interrupted.
IELTS Writing Correction
- 1. Unsupported purpose Original: internal climate Suggested revision: the house Why it matters: The diagram shows heating the house and water, not controlling the whole internal climate.
- 2. Unsupported detail Original: pre-set temperature Suggested revision: a usable temperature Why it matters: The diagram does not mention a thermostat or pre-set temperature.
- 3. Invented structure Original: two stages Suggested revision: a continuous system Why it matters: The diagram does not divide the process into two stages.
- 4. Unsupported term Original: transitory state Suggested revision: initial flow of cold water Why it matters: This technical stage is not shown in the visual.
- 5. Unsupported term Original: steady state Suggested revision: regular circulation Why it matters: This is not labelled or implied clearly by the diagram.
- 6. Unsupported source Original: local water utility supplier Suggested revision: cold water supply Why it matters: The diagram only labels cold water entering the house.
- 7. Comma splice Original: water, this fluid is then pumped Suggested revision: water. This fluid is then pumped Why it matters: These are two independent clauses.
- 8. Diagram label Original: some tubes Suggested revision: small tubes Why it matters: Use the label shown in the diagram.
- 9. Awkward definition Original: equipment used for exchanging temperature Suggested revision: devices that transfer heat Why it matters: This is more natural and accurate.
- 10. Invented detail Original: a specific volume according to an engineering design Suggested revision: Delete Why it matters: This information is not shown in the diagram.
- 11. Unsupported sequence Original: continually repeats until the water gets a predefined temperature Suggested revision: circulates through the radiators and returns to the boiler Why it matters: The diagram shows circulation, not a repeated filling stage.
- 12. Unsupported cause Original: thanks to the high pressure Suggested revision: Delete Why it matters: The diagram does not mention pressure.
Suggested Rewrites
- internal climate the house
- pre-set temperature a usable temperature
- two stages a continuous system
- transitory state initial flow of cold water
- steady state regular circulation
- local water utility supplier cold water supply
IELTS Writing Criteria Scores
Detailed feedback by IELTS writing criterion after the annotated essay.
Task Achievement
The response describes a heating system, but it invents unsupported stages, pressure changes, engineering design details, and a reserve-water function. It misses the simple flow shown: cold water enters, fills a storage tank, passes through a boiler, circulates through radiators, and supplies hot water to taps.
Base every stage on a labelled part of the diagram and remove explanations about pressure, transitory states, and service interruptions.
Coherence and Cohesion
The answer is organized into stages, but those stages are not shown in the diagram, so the structure partly misleads the reader. Several long sentences are hard to follow.
Organize the process by actual flow: cold water supply, heating/circulation, hot water use, and overflow.
Lexical Resource
The vocabulary range is quite wide, but several technical words are used inaccurately or unnecessarily.
Use simple process vocabulary and the labels from the diagram rather than adding technical explanations.
Grammatical Range and Accuracy
There is a range of complex sentences, but comma splices and awkward clauses reduce control.
Split long sentences and use full stops between independent clauses.