S Plan query

[Dan217]

Hi

I dont know if this has come up before, but I couldn't find anything via the search.

I have decided to have a unvented cylinder fitted to my existing system using a simple S plan.

Straight forward so far !! My existing system is an oil combi, the plumber that came round said it was in perfect condition so it didn't warrant a new system boiler and he would just do an s Plan system joining in the cylinder, which seems fine, however (I am sure he will know this) just through my curious nature, I have been looking at s Plan wiring diagrams, I cant find any that include a combi, the s plan wiring looks very straight forward but there doesn't seem to be any allowance for firing the boiler up, there is a part which goes to the LNE of the boiler but surely that would mean that when either hot water or heating is not required the boiler would be off (I mean no power to it at all) is that correct or have I just got the wrong end of the stick?

I just like to know how this system would fit in to my scenario.

Hope someone can put me straight.

Thank you.

 

[D_Hailsham]

Which boiler (make and exact model) do you have?

 

[Dan217]

Its a Grant combi 90 MkII

 

[Dan Robinson]

The boiler will just think it is doing the heating.

 

[Dan217]

Thanks for the reply.

So I presume that the boiler and cylinder are wired up as the S Plan system with the link replaced where the timer used to go on the boiler and the boiler put on continuous. Therefore allowing the boiler to be switched on as and when hot water or heating is required via the new s plan.

 

[twgas]

Not exactly. The ons from the zone valves will be connected to the connection normally used for just heating.

 

[Dan217]

Thank you for that.

Another question about S Plan.

What would happen if the room stat and the cyl stat both called for heat at the same time ?

Is priority given to one of them or is this something that just couldn't happen?

Thank you.

 

[Dan Robinson]

The capacity of the boiler will be shared between the 2.

However, if the is' still an outlet connected to the domestic waterside of the boiler (advisable), then that will take priority as it does now.