Vaillant ecotec radiators getting hot whilst running hot water

vaillant ecotec diverter valve failure

This was a repair on a Vaillant ecoTEC Pro 28 Combi boiler that I did yesterday in Darton, Barnsley, S75.The issue was that the radiators would start getting hot when the hot tap was being run, which is not an uncommon fault with combi boilers in general.

As far as Vaillant ecoTEC Combi boilers go this is generally less of an issue in my experience, but as with other Combi boilers most of the time it is an issue with the diverter valve which diverts the heat from the main heat exchanger to the radiators or to the hot water.

The fault I came across with this boiler yesterday was indeed a faulty diverter valve, but the valve had failed in a way that I don’t think I have come across before.

The Vaillant ecoTEC Combi models diverter valve design uses a pin which moves back and forth operating a piston which diverts the water flow. The piston and pin is operated via an electric motor. What usually happens on these models is that the pin seal and pin become dry as they have no lubrication. This can cause the pin the get stuck and sometime burn the electrical motor that operates it out.

Silicone grease applied to Vaillant ecoTEC diverter valve pin

silicone grease on vaillant diverter valve
This boiler had been drained down for six months when the house was empty and when filled back up the valve started playing up. on the end of the piston there is a small circlip which secures the piston to the pin, and somehow the circlip had come off. I suspect the piston had got stuck and the motor just forced the circlip off the piston.

So the piston was stuck mid position which meant that when the boiler was firing up for the hot water half of the heat would have been travelling down the flow pipe warming the radiators up at the same time.

This would have resulted in poor hot water performance as well as reduced performance when the central heating was on.

Whenever I service a Vaillant ecoTEC Combi boiler I always apply a little bit of silicone grease to the pin which helps it keep moving freely and help to prevent unwanted call outs for the customer.

The diverter valve is one of many parts I carry as stock for repairs on the Vaillant ecoTEC boiler and I was able to repair and service this boiler in one visit – the customer had their boiler working again in just over an hour.
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Areas where I can repair your Vaillant ecotec pro combi boiler

areas that are covered

I cover a large part of South Yorkshire including most of Sheffield, Rotherham and Barnsley. I also cover a small part of Doncaster.


I cover most of Sheffield including central Sheffield, Chapeltown, Ecclesfield, Grenoside, High Green, Oughtibridge, Thurgoland, Wortley, Aston, Aughton, Swallownest, Todwick, Hillsborough and Stannington.


I cover the whole area of Rotherham including central Rotherham, Brinsworth, Catcliffe, Canklow, Masbrough, Treeton, Whiston, Greasbrough, Kimberworth, Thorpe Hesley, Rawmarsh, Wentworth, Bolton-on-Dearne, Goldthorpe, Thurnscoe, Wath-on-Dearne, Mexborough, Swinton, Kilnhurst, Hooton Roberts, Ravenfield, Thrybergh, Bramley, Hellaby, Maltby, Thurcroft, Wickersley and Braithwell.


I cover most of Barnsley including central Barnsley, Birdwell, Stairfoot, Worsborough, Kendray, Ardsley, Athersley, Monk Bretton, Lundwood, Royston, Brierley, Cudworth, Cortonwood, Great Houghton, Shafton, South Hiendley, Brampton, Darfield, Wombwell, Hemingfield, Elsecar, Hoyland, Jump, Barugh Green, Cawthorne, Darton, Dodworth, Gawber, Mapplewell, Pogmoor, Staincross, Wilthorpe, Worsbrough, Thurnscoe and Tankersley.


I cover a small part of Doncaster including central Adwick, Conisborough, Edlington, Warmsworth and Mexborough.