Try again NO CH but DHW working fine

[Ste38]

Hi i have got a Vaillant VCW GB 242EH boiler about 10 year old it's been brilliant but recently just today for no reason the CH has stopped working, when i had the hot water running(it was very hot as normal)but CH switched off i noticed the CH flow pipe was also hot but radiators cold. I turned off the hot water let the fan stop running so it was quiet then turned the CH on, the th'stat down to a low temp then up until it clicked which is the point the CH usualy switches on, but nothing, when i turn the hot water on the pin off the water section moves up ok & turns the servo valve cam to the micro switch, the pump & the fan switches on, the diverter valve moves to the right & the boiler fires up, so i presume the pin,cam & switch etc is all working, i read on a previous post that if the CH flow pipe gets hot with just DHW working that the diverter valve could be at fault but on another post it said the Vaillant boilers didn't use these as much so i could do with a few pointers, my info is basic as i know nothing about any boiler's except what i can see by watching it & the info off this forum, my backround is in a car parts dept. PS not sure about water or gas pressures i wouldn't know where to start however it has just stopped working & has been for the last 10 years so i can't see water/gas pressure to be a fault when the DHW is running the flames are a good height/colour & the water out the cold tap is at a good pressure so i would like to think they are ok. I take it i would be looking at one or more of the following, Diverter valve, water section or servo valve, oh also this system use to lose pressure so i was often topping it up off the cooling loop so any additives that was in the system all them years ago will probably be diluted to the point of it just being water without additive in the system, could this have any bearing on things many thank's sorry for the long post just wanted to get as much in as possible, regard's Stephen.
Update i have already posted this but didn't get to far hence my repost i have searched this forum & have seen loads of Vaillant help i'm just hoping i can get some pointers as the only advice i have had so far is change it which is all well & good it you've got a couple of grand spare at xmas which i haven't thanks again to everyone for looking.

 

[picasso]

The external controls have to be disconnected and a bridge put between 3 and 4 on the pcb, this will prove if its a boiler fault or an external control fault, as you would be dealing with 240vac it might be better to get someone that deals with boilers every day, could work out cheaper in the end.

 

[Ste38]

Thanks picasso to disconnect the external controls it do i just isolate the boiler take out the black wires in terminals 3 & 4 behind lower front cover then just put a loop in between 3 & 4 as a test???

 

[picasso]

You got it, but as I said be very careful all the connections your using are 240v.

 

[Ste38]

Thanks again Picasso removed the black wires had to mark them up 3 & 4(for when i put them back in), put in a loop using 240v cable swithced on & it fired up straight away diverter valve is now sitting correctly & rads getting warm, many thanks it was getting cold , just not sure now if its the thermostat control dial(Honeywell) or the control box with the clock on for the timer at least i know the boiler is ok.

 

[Ste38]

Just somthing i've thought there in regards to the timer control, it's a Landis & Gyr RWB100 i'm sure when it was switched on & everything working that there use to be a red L.E.D in the bottom right corner as your looking at it, i just realised tonight after doing the 3 & 4 pin test that the L.E.D isn't on the clock is on but that's it , does ths mean it's possibly a timer control box fault???

 

[ratonnastick]

Yes its your programmer at fault.

ps. I thought you agreed it was 15 years old?

 

[Ste38]

Thanks ratonnastick, are the timers easy to fit is it worth changing manufacturer or is the Landis & Gyr quite reliable?? Also is it something i need to do straight away?? or can i keep the test loop in between pin's 3 & 4 just while i'm in the house to keep it warm, the boiler runs just like you've got the thermostat up to the highest setting, i can use the winter/summer rad temp setting control knob on the combi boiler to regulate its temperature to some degree & power it down when i'm not in. The only thing i did notice was the fan seemed to stop on for longer when the boiler had switched off, does the external controls have any bearing on the fan operation?? (the fan works fine using DHW & has always worked fine using the CH in the past) , thanks again.
PS yep sorry rat boiler is 15 year old .

 

[ratonnastick]

Most new single channel programmers will come with a guide to change it from the exsisting , so it should be easy to swop for one of your choice.

Running the boiler with no external controls is not a problem only more expensive.

 

[Ste38]

Your help is much appreciated, i had a bit of a panic on, christmas in Cumbria with no CH not a good mix , just one last question, is there any manufacturer you would recommend to use with regards to buying the timer/programme box??

 

[ratonnastick]

I Would fit a Drayton LP711 but I get them really cheap.

 

[Ste38]

Thanks again for your advice