Vaillant vcw 242 eh. Hot water, but to get heating boiler has to be turned off

[Charles Muscat]

Hi I have a Vaillant vcw 242 eh, the hot water is working well on it and is getting up to a good temperature to flow rate. The problem i am having is with the central heating.

When the thermostat is clicked on it fires up, but if you click it down and then click it back on again the boiler doesn't fire up. The fan and pump continue to run as if it is working but the flame doesn't ignite. If the boiler is turned off from the switch on the front and left for 5 seconds, when the switch is turned back on the boiler fire up straight away.

I have tried turning the hot water on and off while the heating is on and that doesn't disrupt it at all, it is only when the thermostat or the timer is switched off that the heating will not go back on again until the boiler is turned off from the front switch.

When turning it off from the front switch on the boiler the heating works again every time, whether the thermost is in the on position at the point of it being turned on or turning thermostat up after it has been turned on.

2 years ago i had the pump, heat exchanger and water valve changed, becasue hot water wasn't working some of the time. That was all done by BG, because they couldn't find the fault at first, but it was the water valve that was not working intermitantly and not had any problems since, until this.

My main thought was that it could be the saftey switch 251822, but was worried it might be a problem with the pcb as it seems like an electric fault rather than anything else.

The diverter valve microswitches look to be working fine as they completely disingage when the hot water is turned on and move back to fully engaged when hot water is turned off and the heating is being requested.

Any help or advice on this would be really appreciated, i have read through a number of forums, but have not seen anything about this specifically.

Thanks Charlie

 

[Ihavenojob]

Probably normal operation of the anti cycling device.If you turn the stat down and up again, it won't re fire for a set time.

 

[Charles Muscat]

Hi thanks so much for getting back to me so quickly. How long does it usually take for the anti cycling device to let it fire up again?

 

[Ihavenojob]

Hi thanks so much for getting back to me so quickly. How long does it usually take for the anti cycling device to let it fire up again?

If yours is the one I am thinking of, anything up to about 7 minutes. Turn it off and on again, if it hasn't come back on after 10 minutes, it may be one of the PCB's.

 

[Charles Muscat]

Thats great thanks i'll check that to see if thats the problem. Although i have had my gf say that it was off for a few hours one time, but good to know i have to wait for it if i am testing it. I have read something about the screw on the front being used to adjust the anti cycling, is that correct and if so would turning it towards the - side make this time shorter?

 

[Ihavenojob]

Thats great thanks i'll check that to see if thats the problem. Although i have had my gf say that it was off for a few hours one time, but good to know i have to wait for it if i am testing it. I have read something about the screw on the front being used to adjust the anti cycling, is that correct and if so would turning it towards the - side make this time shorter?

If it has it. There were 2 variations of PCB's used. If it has a silver screw with + and -, then it can be adjusted, the adjuster is behind the silver screw, and yes,- is shorter.

 

[Charles Muscat]

That's good to know I will try and adjust it so that i don't have to wait so long for it to fire up again or not. Do you think that there is any chance of it being the safety switch 251822? or the NTC sensor?

Also if it is the pcb's do you think that the problem is most likely dry joints? or do sometimes they need replacing completely?

Thanks again for all your help and adivce about this.

 

[Ihavenojob]

That's good to know I will try and adjust it so that i don't have to wait so long for it to fire up again or not. Do you think that there is any chance of it being the safety switch 251822? or the NTC sensor?

Also if it is the pcb's do you think that the problem is most likely dry joints? or do sometimes they need replacing completely?

Thanks again for all your help and adivce about this.

I doubt it's the safety switch or sensor, as the boiler fires when you turn the boiler off and on. Trying to repair dry joints on these would be a liability, at least you are getting heat at present.

 

[Charles Muscat]

That's great to be able to rule the switch and sensor out. I'll take your advice on the PCB then and just bear with it if it needs to be switched on and off and isn't just the anti cycling and me being impatient that's the problem.

Thanks so much for your help and quick responses!

 

[Gasguru]

The book quotes a default time of 5 minutes for the anticycle time but it can be adjusted from 1 to 12 mins...perhaps with age the setting has drifted.

 

[Charles Muscat]

The book quotes a default time of 5 minutes for the anticycle time but it can be adjusted from 1 to 12 mins...perhaps with age the setting has drifted.

Thanks for checking, that's good to know, i will try and adjust it right down and see what happens.