Hot Water not hot in Unvented System

[arh]

Hi

I have a vaillant system bolier with a Unistor Cylinder.
Everything was working fine until the cold supply was turned off for a few hours due to a water main issue.
When the water came back there was some air in the boiler that my plumber took out by unscrewing the small cap. He left and that evening the pressure dropped on the boiler. I filled it again and pressure is now ok. The hot water temperature is not right as water is not getting hot and just staying lukewarm. I called him but he is not available to come back for a few days...
I will try to set the zone valve to manual to see if this is failing but I suspect there is still air. What else can I check? Could there be air in the cylinder or somewhere else?

Thanks.
ARH.

 

[gas4you]

Your description is a bit vague. Where is the cap your plumber let the air out of? Hopefully the one next to the unistor. Sounds as tough it could be a partial airlock, although a mains water issue should not affect your system boiler unless system was drain.

Has your Unistor/system boiler been wired via the Vaillant VR65 connection unit? If so check the hot water temp dial on the boiler, top one, set this to between 55 or 60.

 

[arh]

Hi
The air was let out from the boiler by unscrewing the small cap - looks like valve cap on car tyre.
Where can I release the air from the Unistor?
I had misleading info on the hot water temp guage - one plumber said to leave it to zero as thermostat on unistor would set the temp while other plumber advised to set it to 60C. Originally I had this set to zero. Will try moving to 60.
Thanks.

 

[gas4you]

I hope you don't mean the car tyre valve on the red expansion vessel in the boiler

 

[arh]

Hi

No the cap at near the back of the boiler near the red pull button for releasing excess water.
My system is half working but the pressure keeps dropping. When I fill the boiler I can hear air in the pipes.
Thanks.

 

[gas4you]

If your pressure keeps dropping then it sounds like you have a leak in the system. You need to find this and correct before you can start fault finding in earnest.