Vaillant ecoTEC PRO 28 leaking diverter valve repair


Vaillant ecoTEC PRO 28 leaking diverter valve repair – Thurgoland, Sheffield, S35.

This was just supposed to be a standard service on a boiler which I serviced a couple of years prior. When I was checking the boiler over I noticed that the diverter valve was leaking slightly when it was moving between domestic hot water and central heating mode.

Diverter valves can and do leak on these ecoTEC combination boilers which is why it is something I always check on a service.

There was some evidence of a small leak but the boiler hadn’t been leaking much as it had been sat in hot water mode all summer and the diverter had not been moving as the central heating had not been used for a while. Come winter when the valve would have been switching over between heating and water a lot, the valve would have started to leak consistently and would have resulted in a small drip from the bottom of the boiler. The boiler would have been losing pressure as a result.

I gave the customer the option to replace the diverter valve. As it was a part I carry as stock for repairs, this was a problem I was able to fix there and then. Usually these valves aren’t leaking when I inspect them on a routine service. When they aren’t leaking, I just lubricate the pin with silicone grease to help keep it moving freely as I have found they sometimes start to seize up.

The Vaillant ecoTEC’s have some nice features which make them easier to work on. There is a setting(P6) which puts the diverter valve in mid position which aids with draining or refiling the appliance. Once filled another program(P0) can be used to purge the air out of the boiler before you fire it back up. Once fired back up, programs P1 and P2 can be used respectively to test the appliance’s maximum and minimum functions.

The whole point of a service is to make sure an appliance is working safely first of all. Secondly the components that actually make the appliance work and keep the appliance running should be serviced and replaced if necessary(give the customer the option), if they are failing. On these Vaillant Combi boilers I typically check and recharge the expansion vessel, check the diverter for leaks and operation, test the pressure sensor and determine how well the pump is working. These are vital components which make the boiler work and are often overlooked on a “service”.



  1. I have had the diverter valve replaced on my EcoTec PRO28 and since then the central heating wont work. The service engineer has removed the in line filter and it was clean. The pump has been removed and checked for function. Both isolation valves have been removed and checked. When the heating is called for the boiler fires up and the system heats up rapidly and within 40 seconds the egg timer shows on the display. The central heating was working perfectly prior to replacing the leaking diverter valve. Could it be a system blockage (i think unlikely) or could it be a faulty recirculation valve.

    1. If it was working ok before then it’s probably not a blockage the egg timer is the anti cycling programme I’m assuming he’s checked there’s no issue with the diverter valve he could try resetting the printed circuit board to factory settings aside from that he’s best off speaking to vaillant for some technical advice if he hasn’t already

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