How Aren protected a customer in vulnerable circumstances after discovering an incorrect flue and multiple serious defects across an existing boiler installation.

Project overview

Aren Heating & Plumbing attended a London property where the customer believed their boiler was safe and correctly fitted. Inspection showed that this was not a single minor defect: the boiler, flue, valves and associated pipework contained several serious installation problems.

The customer was in vulnerable circumstances and had relied on the original installer to provide safe, competent work. They had paid for a boiler installation that was subsequently found to contain multiple defects, including a flue made for a different boiler manufacturer.

Our immediate role was to protect the customer, explain the findings clearly and prevent the unsafe appliance from continuing to operate. We then documented the concerns, referred the installation to Gas Safe Register and planned the corrective works needed to return the property to safe working order.

The most serious defect: the wrong flue

The boiler was a Baxi appliance, but it had been connected to a Vaillant flue system. Boiler flues are safety-critical, manufacturer-specific components designed and tested as part of the appliance installation. Components cannot simply be treated as interchangeable because they appear similar or connect physically.

The flue carries combustion products safely outside while supporting the appliance’s combustion process. Using an incorrect system means the installation cannot be relied upon to perform as the boiler manufacturer designed and specified. Aren therefore treated the boiler as unsafe and it could not remain in service.

Further defects identified

The inspection found a wider pattern of defective workmanship beneath and around the boiler:

• Incorrect isolation valves fitted beneath the boiler.
• Hot and cold connections configured incorrectly.
• An incorrect return isolation valve installed.
• Associated boiler pipework requiring alteration.
• Gas pipework without adequate clipping and support.
• Condensate pipework without adequate clipping and support.
• A gas cooker without a stability chain, resulting in an At Risk classification.

Taken together, these findings confirmed that the installation required substantial corrective work rather than a cosmetic adjustment or a simple flue change.

Immediate action to protect the customer

A gas tightness test was carried out and the installation was confirmed sound at the time of testing. Because the boiler had the wrong manufacturer’s flue, the gas supply beneath the appliance was capped and the boiler was left safely isolated.

A further tightness test was completed after isolation and was satisfactory. The cooker was also turned off after the missing stability chain was identified. The customer was advised not to use the affected appliances until the necessary corrective works and safety checks had been completed.

Reporting the installation

The concerns were serious enough that a written report was prepared and the installation was referred to Gas Safe Register. This created a formal record and allowed the appropriate independent body to consider the circumstances of the original gas work.

Gas Safe Register accepts concerns about unsafe or badly completed gas work and can investigate installation defects against relevant manufacturer instructions and industry technical standards. The case study does not speculate about who carried out each element of the original work or the outcome of any separate investigation; it records what Aren found and the action we took.

The remedial plan

• Remove the incorrect Vaillant flue and install the correct Baxi flue system.
• Install a new boiler connection pack and correct the isolation arrangements.
• Alter the pipework beneath the boiler to create the correct connections.
• Clip and support the gas and condensate pipework correctly.
• Install a stability chain to the gas cooker.
• Recommission and comprehensively test the boiler, cooker and gas installation.

Correcting the installation

Aren returned with the correct components and began by removing the incompatible flue. A correct Baxi flue was installed and sealed internally and externally in accordance with the required arrangement for the appliance.

The boiler was drained, the incorrect isolation valves and defective section of pipework were removed, and a new connection pack and isolation valves were fitted. The pipework beneath the boiler was altered to provide the correct connections, while the gas and condensate pipework were properly clipped and supported.

A stability chain was also fitted to the cooker, resolving the movement risk identified during the first visit.

An additional fault found during the repair

While completing the remedial works, the engineer identified that the boiler filling loop was passing and leaking. This fault had not formed part of the original scope, but leaving it in place could have caused continuing water loss or pressure-related problems.

The defective filling loop was removed and replaced before the installation was recommissioned. This is an important part of Aren’s approach: once work begins, we continue assessing the system rather than assuming that the defects already listed are the only ones present.

Final commissioning and safety checks

• Visually inspected the boiler, new flue, cooker and gas meter.
• Tested the boiler’s safety devices.
• Took flue-gas readings and confirmed satisfactory results.
• Tested the cooker’s safety devices and confirmed satisfactory operation.
• Completed a final gas tightness test successfully.
• Checked the carbon monoxide and smoke alarms and confirmed they were operational and in date.

The outcome

The boiler installation was comprehensively corrected. The incorrect manufacturer’s flue was removed, the correct Baxi component was installed, the defective boiler connections and valves were rebuilt, and the unsupported pipework was secured.

The cooker stability issue was resolved and the additional leaking filling loop discovered during the work was replaced. The boiler and cooker then passed the required operational and safety checks, and the gas installation passed its final tightness test.

The customer was no longer left to manage a confusing list of defects alone. Aren made the immediate risk safe, documented the concerns, completed the remedial work and provided a clear, tested outcome before returning the appliances to use.

Protecting customers in vulnerable circumstances

Customers can be vulnerable for many reasons, and those circumstances do not need to be disclosed publicly. What matters is recognising when someone may need additional clarity, reassurance or practical support.

In this case, Aren used plain language, separated the immediate safety action from the permanent repair, documented the defects and followed the job through to a completed solution. The emphasis remained on the customer’s safety and restoring a dependable installation.

Why correct boiler installation matters

Boilers must be installed using the correct appliance components and in line with the manufacturer’s instructions and applicable gas-safety requirements. A flue, valve or connection should not be accepted simply because the boiler fires or produces heat.

Aren Heating & Plumbing investigates unsafe and poorly completed boiler work across London. We can make an appliance safe, document the defects, plan the necessary remedial work and recommission the installation after correction.

Frequently asked questions

Can a Vaillant flue be used on a Baxi boiler?

No, not unless the appliance manufacturer explicitly specifies that exact component as approved for the boiler. Flue components form part of the appliance installation and must match the manufacturer’s instructions. On this job, the Vaillant flue was removed and replaced with the correct Baxi system.

Why is an incorrect boiler flue dangerous?

The flue must safely carry combustion products outside and support correct combustion. An incompatible or incorrectly assembled flue may not seal, connect or perform as designed. A boiler should not be left operating where the flue installation cannot be confirmed as correct.

What happens when an engineer finds an unsafe gas appliance?

The engineer follows the applicable gas-industry unsafe-situations procedure, explains the risk and takes the steps required to prevent unsafe use. The precise action depends on the defect and classification. In this case, the boiler supply was capped and the appliance was left safely isolated.

Can concerns about previous gas work be reported?

Yes. Gas Safe Register provides a route for reporting unsafe, badly completed or suspected illegal gas work. It may inspect work within its remit against manufacturer instructions and relevant technical standards. Gas Safe Register does not decide ordinary financial or contractual disputes.

Why was the cooker turned off?

The cooker did not have a stability chain and was classified At Risk. A stability device helps prevent a freestanding cooker from tipping or moving in a way that could strain the gas connection. A chain was fitted during the remedial visit and the appliance was safety-tested.

Why was the filling loop replaced?

The existing filling loop was passing and leaking. Because this was identified while the boiler was already being corrected, it was replaced before final commissioning rather than leaving a further known fault in the installation.

Does a working boiler mean the installation is safe?

No. A boiler may light and produce heating or hot water while still having faults with its flue, gas supply, safety controls, pipework or installation. Safety depends on correct components, installation, testing and ongoing servicing, not operation alone.

Can Aren inspect or rectify a boiler installed by another company?

Yes. Aren can inspect existing boiler and gas installations, identify defects, make unsafe appliances safe and quote for appropriate remedial work. Where concerns fall within Gas Safe Register’s remit, they can also be documented and referred through the correct reporting route.