We were there for an annual service, and the customer mentioned the boiler was leaking and the heating was staying on with nothing asking for it. The diverter valve had rust and corrosion around its ports, so we replaced it.
We visited a Vaillant ecoTEC pro 28 combi in Solihull for its annual service, and the customer mentioned two problems: the boiler was leaking, and the heating was staying on even when nothing was asking for heat. With the case off, the diverter valve, the valve that switches the boiler between heating and hot water, had rust and corrosion around its ports, and there was rust staining in the base of the case below it. A diverter valve in that state accounts for both problems, so we replaced it with a new one. We checked the expansion vessel charge and finished with a flue gas analysis: a CO/CO2 ratio of 0.0005, comfortably inside the limit.
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Basic service £95, intermediate £125, full strip-down £185.
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.
We visited a Vaillant ecoTEC pro 28 combi in Solihull for its annual service. When we arrived, the customer mentioned two problems: the boiler was leaking, and the heating was staying on even when nothing was asking for heat. A service is a set of checks on the boiler and its safety, and it is also the best time to look into anything the customer has noticed.
With the case off and the control box lowered, there was rust staining in the base of the case. The diverter valve, the valve that switches the boiler between heating and hot water, had rust and corrosion around its ports. You can see it out of the boiler in the third photo.
That accounts for both problems. The diverter valve is what decides whether the boiler's heat goes to the radiators or to the hot water. Corroded seals at its ports let water out, and a valve that is sticking in the heating position keeps sending heat round the radiators even when the thermostat is not asking for it.
We replaced the diverter valve with a new one, in the fourth photo, and put the hydraulics back together. We checked the expansion vessel charge with a pump gauge, which read 1.00 bar, and finished with a flue gas analysis: CO 44 ppm, CO2 8.9% and a CO/CO2 ratio of 0.0005, comfortably inside the limit.
Our boiler servicing page explains what each level of service includes. We also serviced another Vaillant ecoTEC pro 28 in Kitts Green, where checking the flue turned up a problem in the loft.
A basic annual service is £95, intermediate £125 and a full strip-down £185. Parts found worn during a service, like a diverter valve, are quoted before we fit them. Details are on our price list.
It switches the hot water from the boiler between the heating circuit and the hot water heat exchanger. When you turn on a hot tap it sends the heat to your hot water; the rest of the time it sends it round the radiators. When one sticks or fails you can lose heating, hot water, or both.
On a combi boiler a common cause is a diverter valve sticking in the heating position, which is what we found here. A faulty room thermostat, timer or wiring can do the same. It is worth getting checked, because it wastes gas and can mean the hot water side is not working properly either.
A service is the time to find wear before it becomes a breakdown. If we find a part in poor condition we show you and quote before fitting anything. Doing it on the same visit saves a second callout later, often in the middle of winter.
It measures what the boiler is burning and putting out of the flue, including carbon monoxide and carbon dioxide. The CO/CO2 ratio tells us how cleanly it is burning. Here it read 0.0005, comfortably inside the limit.
Once a year. Vaillant needs an annual service to keep the warranty valid, and it is the only way to catch problems like this one early.
Job attended and photographed by our engineers, October 2026. Written up by Saeed Iqbal, the engineer who leads Synergy Gas & Plumbing (Gas Safe registered 594385). More of our work in the area is on our Solihull page, and every job we write up is on the case studies index.
From £95
Basic service £95, intermediate £125, full strip-down £185.
No travel charge within 10 miles of B20 2JS. Further out, £2 per mile may apply — always agreed before anything is booked.
A routine annual service: condensate trap and magnetic filter cleaned, clean combustion readings. Following the flue into the loft, we found it held only by metal banding with the joint clamps unscrewed. Warning notice left, quote accepted, return visit booked.
Read the case studyThe right-hand manifold inside a Worcester Greenstar 28i Junior was leaking. We diagnosed it, tracked the part down locally, fetched it and fitted it the same day. Customer extremely happy.
Read the case studyThe boiler was showing an H09 fault. We diagnosed a faulty circuit board and, with the board on the van, had the customer back up and running on the same visit.
Read the case studyWe check the whole installation, flue included, and tell you straight what we find. Anything that needs putting right is quoted before it goes ahead.
