Vokera Synesti 35, hot water fine, no central heating

[davidsl500]

Hi Peeps,

Vokera Synesti 35 Combi boiler

Hope you can give me a bit of guidance on my present boiler issue. The DHW works fine and is used regularly each day all year round. The central heating is only used during the winter months and was tried about a month ago for an hour or so and was okay then. Now the CH is not working as it should and appears to be a boiler related issue.

The symptoms are: Central heating turned on and the boiler lights and runs for about 15 seconds or so and then the flame switches off. The pump can be heard running constantly and the boiler will finally light again and go though the same cycle again if left on. The rads get a little warm over a period of time from the briefing firing. The DHW is fine and can be run for 15-20 minutes without any issues.

I am thinking that this is a problem with the diverter valve / motor. My thoughts being that it is not opening fully and thus the boiler is switching off as it reaches the set temp becuase the water is not circulating at the rate it should? This combi boiler is one that constantly tops its small integral tank to provide instant hot water on the DHW side.

I am thinking a start point maybe to fit an overhaul kit 01005127? I am not familiar with the Motorised Valve R2905 - is it possible that these can fail such that they only partially open the diverter and thus the overhaul kit is not required and I should go straight for a motor replacement?

Any diagnostic procedures or guidance would be appreciated, thanks

 

[Agile]

Have you actually felt any water pipes when it does not provide the CH?

If you turn the boiler power off for a couple of hours and put it on to central heating then will it run a little longer as it perhaps preheats the hot water parts?

 

[davidsl500]

Yes it does last a little longer if the boiler is left to go cold. The central heating pipes and some rads get slightly warm after a long period of time probably due to the short firing here and there.

I can hear the motorised valve motor whirring and clicking to a stop after a short while when I rotate the boiler from ch to dhw only and back again. Tonight I gave the diverter housing a bit of a tap or two whilst switching between the 2 modes. It did fire and keep lit for about 15 minutes or so but having gone back to it the boiler had gone out again - bugger! Its now back to lighting for 15 -20 seconds - temp gauge hits about 71 and boiler clicks off.... No hot water was drawn whilst the boiler ran for the 15 minute spell.. apart from right at the start when I ran a hot tap to see if the valve actuated and then moved back again - which it did