Project Overview
David, a homeowner in Palmers Green, North London, N13, contacted Plumb London following a boiler breakdown at his property. Our engineer attended site and identified multiple faults across an ageing Biasi M90E non-condensing combination boiler, a unit more than 23 years old and well beyond its serviceable life. Given the extent of the faults and the age of the appliance, a full boiler replacement was the only sensible course of action. The existing unit was decommissioned and replaced with a brand-new Vaillant ecoFIT Pure 825 combination boiler, complete with a new vertical flue assembly, system filtration, scale protection, updated controls, and a full recommission of the central heating system.

The Client’s Brief
David needed an urgent but thorough resolution to a boiler that had developed a number of simultaneous faults. His requirements were:
- A reliable, efficient replacement boiler suitable for a domestic property
- Minimal disruption to the household during installation
- A product backed by a strong manufacturer’s warranty for long-term peace of mind
- Updated heating controls for improved day-to-day usability
- A fully compliant, Gas Safe registered installation
Our Survey & Recommendations
On attending site, our engineer carried out a thorough inspection of the existing Biasi M90E combination boiler and the wider heating system. The findings were significant:
- The diverter valve was faulty, meaning the boiler couldn’t reliably switch between central heating and hot water functions
- Flue gas analysis revealed an excessively lean combustion mixture, too much air in the flue gases, indicating incomplete combustion and a potential safety concern
- The automatic air vent was leaking, introducing air into the system and compromising performance
- The boiler was prone to overheating, suggesting further internal degradation
- The unit was confirmed to be over 23 years old, significantly beyond the 10 to 15 year lifespan typically expected of a combination boiler
Our engineer’s recommendation was clear: given the volume and severity of the faults, and the age and non-condensing specification of the appliance, repair was neither cost-effective nor advisable. A full replacement with a modern, high-efficiency condensing boiler was the right course of action.
Planning & Preparation
Following the site survey, we prepared a full scope of works and quotation for David’s review. He was given adequate time to consider the proposal and seek any further information before confirming his decision to proceed. Once approved, installation was booked in and the necessary materials were sourced and allocated, with no significant delays during the pre-project phase.
The Work We Carried Out
- Isolated necessary supplies and fully drained down the system
- Decommissioned and removed the existing Biasi M90E boiler, flue and associated components
- Carried out an Adey Magnacleanse power flush in accordance with BS 7593
- Supplied and installed a new Vaillant ecoFIT Pure 825 combination boiler, with a 10-year manufacturer’s warranty
- Supplied and installed a new vertical flue assembly, comprising two 1m extensions, two 45-degree elbows, and a roof penetration collar, with all necessary accessories to current standards
- Altered pipework to accommodate and connect to the new boiler
- Completed all plumbing and electrical connections
- Ran a new condensate pipe externally to the designated rainwater drainage point
- Installed a new Vaillant 22mm boiler protection filter on the system return
- Installed a new 15mm inline scale reducer on the incoming mains supply
- Refilled the system and dosed it with scale inhibitor
- Completed full electrical wiring to Part P and Part L requirements
- Supplied and installed a new Honeywell T3R wireless programmable thermostat
- Supplied and installed a new carbon monoxide detection alarm
- Carried out a gas supply tightness test
- Inspected all radiators for heat emission and balanced the system as required
- Gave a full demonstration of the new system and controls to the client
- Commissioned the installation and completed Benchmark documentation
- Notified Local Building Control and registered the works with Gas Safe
- Removed all waste materials, leaving the site clean and tidy
A formal written testimonial was not obtained for this project. David was satisfied with the standard of work carried out and the thoroughness of the installation process, and the job was completed cleanly and within the agreed programme.
Timeline & Completion
The initial site visit took place on 24 April, and the installation was carried out by our engineers Andrew and Dan Rodger. The work was completed within the programme agreed at the point of booking, with no overruns or unexpected delays.
Challenges & How We Solved Them
Multiple simultaneous faults on an aged appliance
The existing Biasi boiler presented with four concurrent issues: a leaking expansion vessel, a faulty diverter valve, a defective automatic air vent, and abnormal flue gas readings. Individually, each fault would have warranted attention; together, they made the boiler uneconomical and unsafe to repair. Recommending replacement rather than repair avoided David incurring repeated repair costs on an appliance nearing the end of its serviceable life.
Flue route and roof penetration
The new boiler needed a vertical flue configuration with a roof penetration, a more involved installation than a standard horizontal wall terminal. Our team specified and installed a purpose-built flue assembly with the correct extensions, elbows and a roof penetration collar, keeping the installation fully compliant with current flue and gas safety standards.
System water quality
Given the age of the system, water quality was a key concern. Our engineers carried out an Adey Magnacleanse flush in line with BS 7593, removing accumulated sludge and debris from the pipework and radiators. A new system filter and scale reducer were also fitted to protect the new boiler from long-term damage, an essential step in London’s notoriously hard water areas.
Compliance and certification
All electrical work was completed to Part P and Part L requirements, and the installation was fully registered with Gas Safe and notified to Local Building Control. David received complete Benchmark documentation confirming commissioning, giving him a clear record for future servicing, warranty claims, and any future property sale.
The Finished Result
The completed installation gave David a modern, efficient and fully compliant heating system where previously there had been a failing, outdated and potentially unsafe one. The Vaillant ecoFIT Pure 825 is a well-regarded, A-rated condensing combination boiler offering significantly improved energy efficiency over the non-condensing unit it replaced, a meaningful benefit given ongoing energy costs.
The new Honeywell T3R wireless programmable thermostat gives David straightforward, flexible control over his heating schedule, and the carbon monoxide alarm adds an important layer of household safety. With 10 years of manufacturer’s warranty in place and the installation registered with Gas Safe, he has full confidence in the new system from day one. The site was left clean and tidy on completion, and David was given a full demonstration of the new system and controls before our engineers left.
Project Investment
Full project pricing is available on application and varies depending on property size, system configuration, flue route, and any additional works identified on site. This project represented a comprehensive, turnkey boiler replacement, not simply a like-for-like swap.
The scope included system cleansing, filtration, scale protection, updated controls, full certification, and waste removal. Investing in a quality replacement boiler, correctly installed and properly commissioned, delivers long-term savings on energy bills, reduces the likelihood of future breakdowns, and adds value to the property.
Why Choose Plumb London
- Gas Safe registered engineers. All work is fully compliant and certifiable
- Transparent quoting, no hidden costs, no surprises on invoice
- Premium product selection. We specify market-leading brands backed by strong manufacturer warranties
- System-wide thinking. We don’t just replace the boiler, we consider the full heating system
- Clean, professional installations. Site left as we found it, every time
- Fully documented. Benchmark certification, Gas Safe registration and Building Control notification as standard
- Aftercare you can rely on. We stand behind our work and remain available for any post-installation queries
Frequently Asked Questions
How do I know when my boiler needs replacing rather than repairing?
As a general rule, if your boiler is over 10 to 15 years old and developing faults, the cost of repair often outweighs the benefit. Multiple simultaneous faults, as in this case, are a strong indicator that the appliance is reaching the end of its life. Our engineers will always provide an honest assessment and will only recommend replacement when it’s genuinely the most sensible course of action.
What is included in a full boiler replacement with Plumb London?
Our installations are comprehensive. Beyond the boiler itself, a standard replacement includes removal of the old unit, appropriate flue works, pipework alterations, system filtration, water treatment, electrical connections, updated controls where required, and full commissioning with Benchmark documentation. We also handle Gas Safe registration and Building Control notification on your behalf.
Why is a system flush important when fitting a new boiler?
Sludge, scale and debris that build up in older heating systems can significantly reduce the efficiency and lifespan of a new boiler. Carrying out an Adey Magnacleanse power flush in line with BS 7593 ensures the system is clean before the new appliance is connected, protecting your investment and maintaining manufacturer warranty validity.
What warranty comes with the Vaillant ecoFIT Pure?
The Vaillant ecoFIT Pure is available with up to 10 years of manufacturer’s warranty when installed by a registered Vaillant installer and registered with Vaillant at the point of commissioning. Our engineers manage this process as part of every installation, so the client’s warranty is in place from day one.









