Unable to run bath of hot water after boiler change

[sargan]

If the store temperature falls to 60C without any call for heat what starts the store circ pump and does a call for Ch only start it?.

Had just put explanation of that in the thread .... comment #30
When stat open and flow switch active - pump runs to provide stir
If stat is closed ... pump will run and provide boiler with call for Heat signal. (orrespective of flow switch condition)

 

[John.g]

So the DHW boost mode ‘full power mode’ will presumably change the boiler SP to 80C and return it to 70C or whatever when DHW demand ceases?.
The only benefit I see in (if) that is that the store standing losses will be slightly lower than maintaining it at 80C at all times.

Have you tried the pump on increased speed and increased the store stat SP??.

 

[ShaunCorbs]

As soon as you use hot water the boiler should start up with a max store drop of 5 degrees

 

[sargan]

So the DHW boost mode ‘full power mode’ will presumably change the boiler SP to 80C and return it to 70C or whatever when DHW demand ceases?.
The only benefit I see in (if) that is that the store standing losses will be slightly lower than maintaining it at 80C at all times.

Have you tried the pump on increased speed and increased the store stat SP??.

My ‘understanding’. (No guarantee I‘m right)
is that the boiler max burn temp does not change.
What changes is that the ‘cylinder demand boost’ switches boiler to Hot Wafter mode ..
which means direct full power, no modulating.
when ‘cylinder demand.boost’ ceases boiler switches back to ordinary mode, but still set to 80 as max temp.

I have increased pump speed to ‘3’. I am unable to increase Store above 60C until I fit the temperature blending valves … candy risk damage to UFH pipes.

 

[ShaunCorbs]

Too late as tbh the ufh shouldn’t be running at 60 or even 50 you sure there isn’t a blending pump set on the ufh picture ?

 

[John.g]

Should have said the boiler SP.

 

[sargan]

Too late as tbh the ufh shouldn’t be running at 60 or even 50 you sure there isn’t a blending pump set on the ufh picture ?

Absolutely no blending valve on heating circuit .. though I may add one. The system has worked fine until the boiler change. This is the system schematic - no blending

 

[ShaunCorbs]

No but it’s at the bottom of the store so only 40/45 dc flow temp

 

[sargan]

It's physically about 200mm above the flow return pipe, and set to 60C
Store does get to 60C and then stat opens.

 

[John.g]

How is the system running since you increased the pump speed?