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 the houseinternal climate and tap water at a a usable temperaturepre-set temperature. The process runs through a continuous systemtwo stages, starting at a initial flow of cold watertransitory state until reaching a regular circulationsteady 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 cold water supplylocal 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 pumpedwater, this fluid is then pumped through smallsome tubes and radiators, which are devices that transfer heatequipment 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 Deletea specific volume according to an engineering design, this stage circulates through the radiators and returns to the boilercontinually 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, Deletethanks to the high pressure on the piping circuit, water is transported to a storage tank from the boiler, after water is stored in the tankafter the storage tank is completed, water runs down to a sink and when the pressure again is high enough, water is directed towardswater deviates towards a spare water tank which functions as a tank used to fill the storage tankwater reserve for when the service is interrupted.
Why this response received Band 5.5
Overall, this response shows a reasonable range of process vocabulary and attempts to explain the system in sequence, but the description is not reliably grounded in the diagram. Invented stages, pressure changes, and functions weaken Task Achievement, while long sentences reduce clarity. The main priority is to rebuild the report around the labelled flow—from the cold-water supply through the boiler and radiators to hot-water use—and remove unsupported technical detail.
IELTS Writing Criteria Scores
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.
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IELTS Academic Writing Task 1
The diagram below shows how a central heating system in a house works.
Your response
Write the task yourself, then compare your choices with the annotated response.