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.
Send us the certificate or the engineer's note and we will tell you what the fix involves. Leave a number and we will ring you back — usually within the hour during office hours.
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.
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.
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.
Four taps for a fixed figure.
What do you need?
What sort of job is it?
Here is the price range
Call us — do not wait on a form
We answer enquiries the same working day. If it cannot wait, ring 07413 385767.
Pick a slot online insteadRust at the back of the heat exchanger and a carbon monoxide reading on the analyser, in a house with a young family. We capped the boiler off, told the tenant and landlord, and replaced the cracked flue collector and gaskets with the landlord's permission.
Read the case studyThe old white rail had seen better days. We drained it off, hung a new chrome ladder rail on the same pipework, refilled the system with fresh inhibitor and bled it. One visit, no mess.
Read the case studySeveral engineers and a shower pump had not fixed it. The gate valve on the vented cylinder had snapped inside, turning freely but barely open. A full-bore lever valve in its place, and the tenants had proper hot water pressure for the first time in over a year.
Read the case studyWe find it, fix it and finish with the analyser. Call or WhatsApp us the certificate.
