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The final chapter..…..I have been to Maplin and installed a new DC Solenoid micro switch (massive cost of £1.69). You guys are MUSTARD! DHW and CH work perfectly. Better than new..No tapping or machine gun noise. I have to admit I would not have sorted this problem without the forums...

Tony, I have to admit to all I only used a continuity tester with audio to check the microswitch contacts. Hindsight is a wonderful thing....I should have checked it more thoroughly using digital Ohm meter......Could kick myself.... All the best Bill Bill

Sorry had to go out last night.....Yes you are correct. I should have mentioned that the configuration on the system has TRV's and clock. No room thermostat. The VCW has three differnt ways to control the pump depending on external devices and position the Vaillant pump selector link is in...

Tony, For clarity there are two pins...One is as you say above the DC Solenoid (on Differential Valve). The other is the pin on the DC solenoid which activates the micro switch. Yes you are correct the burner will not light unless the pin retracts on the differential valve (it is as you...

Tony, Wont do the terminology conversion as it looks like Bunnyman has the answer......I think you and I must have the same "investigatory" gene. I don't like guess work and always like to know how things work. Yes you are correct. More knowledge on the old VCW Sine 18T is not going to...

I have taken the DC Solenoid microswitch off and checked it. Seems to work fine. However, if this is a common fault known as "Machine gun" I will order a new one. Only thing which does puzzle me is it doesn't "Machine Gun" when burners are switched off on HEATING. I would have expected the...

Tony, Many thanks for the reply. It is much appreciated. I will answer each of your questions and then offer my thoughts on the problem for you to corroborate or challenge. To simplify correspondence I have cut and pasted your questions below along with answers. Q1. "I know that you...

This is one for the mature and experienced Vaillant heating engineer! Symptom: 28 year old Vaillant Combi VCW-Sine 18 T3WF H in excellent working order. Heating and Hot water work correctly. However, the unit has developed a minor tapping/knocking noise after HOT WATER demand is closed...