A previous engineer had reported a leak on the gas safety check. We found it, deep inside the boiler, and rebuilt the combustion box around a new collector and seals.
A landlord in Stourbridge had a Worcester CDi with a leak reported on its gas safety check by a previous engineer. We attended the follow-up, traced the leak to the condensate collector inside the combustion chamber, where the seals had deteriorated, and replaced the collector and its seals. It is a big job: to reach the collector, the fan, burner and heat exchanger door all have to come out of the combustion box. We rebuilt it, resealed it, tested it and checked the combustion on the analyser, which read 79 ppm of carbon monoxide with a CO/CO2 ratio of 0.0008, well within the safe range. Another happy customer.
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£99 in office hours (Mon–Fri, 8am–5.30pm) covers attendance, diagnosis and the first hour. Parts and any further work are quoted and agreed before we carry on. Out of hours, the price is quoted by phone before we set off.
No travel charge within 10 miles of B20 2JS. Further out, £2 per mile may apply — always agreed before anything is booked. Full price list
Smell gas now? Do not use this form or wait for a reply. Call the National Gas Emergency Service free on 0800 111 999 (24 hours). If you are using a mobile, make the call from outside. Open doors and windows, do not switch electrics on or off, do not smoke or use naked flames, and turn the gas off at the meter if it is safe to do so, unless the meter is in a cellar or basement. Once the supply has been made safe, we can trace and repair the fault.
The landlord of a property in Stourbridge had a gas safety check done by another engineer, who reported a leak on the Worcester CDi but did not fix it. The landlord asked us to attend the follow-up, find the leak and put it right so the property could be signed off.
A leak on a condensing boiler is easy to misdiagnose, because the water usually shows up some way below where it starts. We traced this one up into the combustion chamber. The condensate collector, which gathers the acidic condensate off the heat exchanger and drains it to the trap, had seals that had deteriorated with age, and it was weeping every time the boiler ran.
The collector sits behind everything. To reach it on a CDi the fan, the burner and the heat exchanger door all have to come out of the combustion box, and the box has to be cleaned before anything goes back. You can see the scale of it in the photos: the burner assembly laid out on the side of the boiler, and the combustion box empty with the staining from the old leak on its floor. We fitted the new collector with new seals, cleaned the box, rebuilt the burner and fan assembly with fresh gaskets, and reconnected the condensate run.
Then the part that turns a repair into a safe boiler. We ran the boiler up and put the flue gas analyser in: oxygen 3.8%, carbon monoxide 79 ppm, carbon dioxide 9.7%, and a CO/CO₂ ratio of 0.0008. Those are the readings of a boiler burning cleanly, and they went on the paperwork. Another happy customer, and a landlord with a boiler that passes.
Condensate is mildly acidic. A collector that leaks inside the boiler drips it onto the floor of the combustion box, the seals and the metalwork, and over time it corrodes what it touches. Left long enough it reaches the parts that keep flue gases out of the room. That is why a gas safety check flags it, and why the right answer is to fix the source rather than mop up the trap. It is also why we always finish with the analyser, so the landlord has a reading rather than a promise.
A gas safety check that reports a fault is only half the job. The certificate cannot be issued cleanly until the fault is fixed, and a tenant is left with a boiler that has a known problem. We do the check and the repair, and where a fault turns up on our own CP12 visit we will usually fix it there and then, because we carry the common parts. Our landlord page covers how we bundle the certificate, the service and any repair into one visit and one invoice.
In office hours a boiler repair callout is £99, which covers attendance, diagnosis and the first hour, with parts charged on top and quoted before we fit them. A strip-out like this one takes longer than an hour, and we tell you the labour before we start. A landlord gas safety certificate is £90 for a boiler and cooker. Full details are on our boiler repair and gas safety certificate pages.
This is one of several Worcester repairs we have written up. Our Worcester boiler repair page covers the faults we see most on Greenstar boilers, with every job photographed.
It is the tray inside the combustion chamber that collects the acidic condensate running off the heat exchanger and drains it to the condensate trap and out of the boiler. Its seals harden with age and heat, and when they fail the collector weeps into the combustion box. Reaching it means removing the fan, burner and heat exchanger door.
A gas safety check is an inspection, not a repair. The engineer records what they find and it is then for the landlord to have it put right. Some engineers only do the check. We do both, and where a fault comes up on our own CP12 visit we will normally fix it on the spot.
Not immediately, but it is not something to leave. Condensate is acidic and corrodes what it drips on, including seals and the combustion box, and water inside a boiler finds its way to the electrics. The safety risk grows the longer it runs, which is why a check flags it and why we fix the source rather than the symptom.
The analyser measures what is in the flue. Oxygen at 3.8% and carbon dioxide at 9.7% show the boiler is burning with the right amount of air, and 79 ppm of carbon monoxide with a ratio of 0.0008 is a clean burn. Manufacturers set limits for these figures, and a boiler outside them needs attention. We take the reading on every repair and service, and it goes on your paperwork.
Job attended and photographed by our engineers in Stourbridge, March 2026. Written up by Saeed Iqbal, the engineer who leads Synergy Gas & Plumbing (Gas Safe registered 594385). More recent jobs in the area are on our Stourbridge page, and every job we write up is on the case studies index.
£99 diagnosis + first hour
£99 in office hours (Mon–Fri, 8am–5.30pm) covers attendance, diagnosis and the first hour. Parts and any further work are quoted and agreed before we carry on. Out of hours, the price is quoted by phone before we set off.
No travel charge within 10 miles of B20 2JS. Further out, £2 per mile may apply — always agreed before anything is booked.
Heat exchanger stripped and cleaned on a Viessmann that is showing its age, then the Tempest cylinder serviced on the same visit. Customer given a straight view on when to start planning a replacement boiler.
Read the case studyA London landlord booked online for a tenant with no hot water from an Intatec Hiper HIU. The pressure independent control valve was sticking and the strainer behind it was seized and packed with dirt. Freed, stripped, cleaned and refitted; a new valve booked for a return visit.
Read the case studyThe main heat exchanger had failed on a boiler that had done 17 years, so the numbers pointed one way. Like-for-like swap into the same cupboard, Worcester magnetic filter fitted, system dosed, guarantee registered.
Read the case studyWe find it, fix it and finish with the analyser. Call or WhatsApp us the certificate.
