Vokera option HW issue

[jgmgasservices]

Evening Chaps,

Got a Vokera option. Hot water runs hot then cold. Boiler not modulating to low on HW. High and low gas pressures are correct,
Replaced DHW thermister. Its a twin pass Heat ex
Thinking blockage maybe?

Any help appreciated

Cheers

 

[diamondgas]

Not familiar with the boiler ... however IF the primary o/heat is governed by the heating sensor then it could be faulty tripping the flow temp prematurely? Just a guess... Otherwise I'd be thinking as you are?

 

[jgmgasservices]

Cheers Diamond

I will try a primary NTC. Ill let you know how I get on.

 

[bewsh]

Does it work ok if you take the combustion case off? Could be an air pressure issue - dirty fan/venturi?

 

[diamondgas]

Cheers Diamond

I will try a primary NTC. Ill let you know how I get on.

I gave the instructions a glance over and there's a separate o/heat & flow sensor so chances are its dropping out on o/heat. Either that could be faulty or blockage? instructions also mention that the flame will extinguish if the hot water temp gets to 5DegC above point .. Does this occur?

 

[jgmgasservices]

Going back next week with a primary NTC and o/heat stat. Will change these check/clean fan and venturi. Also has two flexible connections to heat ex, will check these for blockages. Will let you know how i get on.

Thanks for advise

 

[diamondgas]

Going back next week with a primary NTC and o/heat stat. Will change these check/clean fan and venturi. Also has two flexible connections to heat ex, will check these for blockages. Will let you know how i get on.

Thanks for advise

Aha! I know the one now! Only ever worked on one and I had to change those flexi's coz they were choked up! Horrible Boiler!! Good Luck!

 

[jgmgasservices]

Went back today. Replaced primary ntc cleaned fan and venturi replaced o/heat stat. Still same.

Turns out that every 4/5 mins it cuts power to the fan for just a second. Which means either demand lost or boiler thinks its hot enough.

Dont think its a blockage as pump doesnt run for HW. Temps were fine modulating ok not o/heating. Linked out flowswitch (long shot) still same. Only thing I can think is PCB. Vokera agree.

So another visit req.