Oil fired cooker/boiler

[maltaron]

I have an oil fired cooker/boiler with twin burners. When using cooker only some heat goes to the boiler. The pump is controlled by the boiler temperature and switches at around 50c. If this is driving a Y plan system the with neither DHW or CH selected, then the 3 way valve would default to DHW and put the excess heat to the water. However, I have an S plan system and the hot water valve is switched by the controller via the cylinder stat, and switches on the boiler via its auxiliary contacts. The surplus heat cannot therefore go the DHW. In order to remedy this I propose to use the pump supply to switch the DHW valve, and when DHW is selected send the power to the boiler burner via the cylinder stat rather than the valve contacts. Does this appear OK.

 

[cider]

think you may need a relay in there somewhere.

 

[maltaron]

Thanks cider, Looking at the problem again I think you are correct in that a relay should be used to switch the boiler burner so that the relay replaces the motor auxiliaries.

 

[Tipper]

What make cooker is it?

 

[maltaron]

Stanley Brandon

 

[cider]

put a link up to the wiring instructions and i might be able to design &
email you a wiring diagram if needed

 

[maltaron]

Thanks for your help, Cider, the circuit I have used is fig 29 on page 23 of this manual. http://www.waterfordstanley.com/media/200726/brandonoilhpbinstallationmanual.pdf

without the u/floor heating

I propose to connect the motor of the hot water valve to the pump live, disconnect the brown and orange wires of the valve and connect these to the normally open contacts of a relay, the coil of which is connected across DHW timer (pin 3) via cylinder stat and neutral.

Your comments are appreciated

 

[cider]

Why not use their diagram and just connect interstat (pin 9) to hw valve brown instead ?

 

[maltaron]

Thanks for your interest. The interstat is only live when the boiler is in danger of severe overheating, when it switches on the central heating and removes power from pin 6, thus stopping the boiler. The problem is that currently when the pump switches on with only the cooker burner running the pumped water can only go to the heat sink rads, and just switching on the DHW valve causes the boiler burner to cut in and produce more heat.
Once again, many thanks for your interest.

 

[JBPHS]

Hi, I really think that the interstat should be connected to the live of the motor of the zone valve for the heating zone valve (as per manufacturers instructions, i.e. if using a Honeywell 2-port zone valve it would be the brown wire). Wiring the interstat to the DHW zone valve can will override the temperature control of the DHW. The interstat will open the zone valve (and possibly run the pump using the cookers own control, if wired as per the diagram), but it will not fire the burner as the common to the zone valve (i.e. the grey wire on a Honeywell 2-port zone valve) will not be live (no call for heat).

Hope this helps.