vaillant vcw gb 242 eh

[gaz86]

hi all, last week i changed the DHW heat exchanger on a vaillant GB 242 EH its about the 3rd ive done in the last few years, the others with no problems, this 1 however.... after refilling an checking there was no leaks i thought the worst was over, i then turned the boiler on, the pump ran the fan ran but no ignition. In the end i had a word with 1 of lads in the merchants i use an he told me that you can have lots of problems with air wen refilling, by this point the pump was also on its last legs (which i thought might not be satisfying the pump proving switch) so i swaped that made sure all air was nicely purged and then all worked well.... until today i recieved a call saying the heating isn't working. Ive been back and looked tonight and the diverter although may b a little slow appears to move an switch micro switches as it shud, but the heating is intermittent to fire an only holding in for short periods of time sometimes and other times holds in till it goes off on stat. the hot water works fine still. could it be anything to do with the servo valve i've read about on previous posts? 1 of the connections on this looked a little coroded, but i cant remember which 1 it was or where the pipes came from at the mo
its the none hybrid board and i changed the diverter disc when i did the heat exchanger (which was changed due to leaking)

any advice would be much appreciated
thanks gaz

 

[Deleted member 105431]

most likely a faulty servo or partially blocked/airlocked tubes to servo. I always stick a new aav on as this helps remove air after a draindown.

 

[BGEngineer]

Yeah change the servo valve, it will be the answer to all your problems. The servo valve directs the pressure from the pump either to the front of the diverter diapragm or to the back to move it backwards and forwards depending on whether HW or Heating required. The servo valve itself is moved by the hot water spindle and this is how it changes direction of the flow. I rarely have to change VCW diverter valves but changing the servo is fairly common. Usually when the diverter has had it it wont move at all, but as you have movement, it will just be a case of the servo.

 

[mickyg]

Yeah change the servo valve, it will be the answer to all your problems.

not if the water valve pin is not retracting fully it won't be

 

[BGEngineer]

Very true Micky G, these often get corroded and can hold the servo in the HW mode. If this is the case push down on top of the servo fulcrum and see if it retracts.

 

[gaz86]

ill have a better look at the servo valve tomorrow then an see what its doing, as i've not taken one of these apart on this model of boiler before can anyone tell me is it possible to service/rebuild or is it best just to replace? if they are serviceable any helpful hints or tips?

thanks

 

[holty]

worth a try. have you checked the flue venturis not partially blocked or the aps is working properly.

 

[gaz86]

yeh checked them out early on they all appear fine.

 

[BGEngineer]

Can't, service the servo valve just replace.

Only need to drain system side not domestic

Remove the one screw holding it in position, and remove the 2 electrical leads on the microswitch, then slide the servo right then pull forwards to release.

Remove the 2 pipe securing plates and then pull out the 4 pipes.

This will then give you access to the Hot Water Spindle. As the servo connections are all on the system side not the domestic there is no need to isolate the mains therefore you can check the function o the hot water spindle, opening closing a tap and make sure its retracting fully.

 

[gaz86]

right i'll have a go at that tomorrow and let you know thanks for your help.
one last thing, any rough idea of cost of servo valve as the cost of this job keeps rising was only supposed to be heat exchanger at first then had to have a new pump plus this part on top

 

[BGEngineer]

According to Parts Center its 42.85 ex vat, sure it must be cheaper elsewhere.

Just seen it 38.00 here including VAT

for http://www.uk-plumbing.com/vaillant-servo-valve-012646-p-32746.html

 

[gaz86]

thanks, i just found a price on net for £29.87 so its not extortionate whatever.