Oil & electric Heating wiring

[Norv]

Ive got a situation where I wired a 12KW boiler into a new build & now an oil boiler has got to be installed.

The programmer which is a Horstmann H37XL is controlling the heating at the moment. The customer wants the oil boiler to take over from the 12KW boiler but still have it as a backup

The plumber has suggested removing the pump which goes into the 12KW boiler & 'T'ing it with a motorized valve so water feed is permanent to the oil boiler unless something goes wrong with the oil & they need to use the electric boiler.

Can I use one of the channels on this programmer to do this & any ideas how it would be wired ??

Cheers

 

[ColJack]

it wouldn't be a channel, it would have to be a manual switch surely??
unless the oil boiler has some sort of alarm output or a "running" output that could be used to work with some sort of auto changeover?

if you can get the details of the old electric boiler and the new oil one, or a link to the manuals we might be able to work something out..

 

[Norv]

Ill see if I can find a link

The plumber was on about using some sort of relay in the circuit but I didnt quite know where. I didnt dismiss this until I got home & had a think. Cheers.

 

[flameport]

One way is to use a 3 port diverter valve containing an auxillary changeover switch, such as the Honeywell V044F1000
This would be plumbed in before both boilers, so that water either flows through the oil one OR the electric one, (never both). Note this valve is NOT the same as the 3 port one usually found in heating systems.

The default is port B on the valve, which should be for the oil boiler.
Port A for the electric boiler, which will only be open when the valve is energised. The 3rd AB port is obviously the flow from the rest of the system.

You need a switch to select oil/electric, such as a normal 1way lightswitch.

Wiring would be:
COM on the switch - live
L1 on the switch = valve brown

Valve blue - Neutral
Value green/yellow - Earth
Valve orange = the 'demand' output from the rest of the system (this is what normally connects to the boiler to indicate heat is required.)
Valve grey - demand terminal on the electric boiler.
Valve white = demand terminal of the oil boiler.

How it works:
The programmer and other controls activate the 'demand' wire in the usual way, so the boiler only operates when required.

With the switch OFF, the oil boiler is selected. The valve is not energised and therefore is held at position B by the spring inside it, so water flows through the oil boiler only.
The 'demand' wire is switched to the oil boiler only, so the electric one won't work.

With the switch ON, the electric boiler is selected.
The valve motor is powered via the brown wire, and the valve will move to position A..
When the valve reaches that position, water will flow through the electric boiler only, the changeover switch in the valve will operate and the 'demand' wire will be switched to the electric boiler, so the oil one won't work.

The single pump will need to be connected to both boilers. If for some silly reason the boiler pump output is not via a relay, then you will need to fit a relay to the pump output, and use the relay contacts to switch the pump on.

 

[Norv]

Excellent. Thanks for the replies

Is that definately the part no. for the diverter valve. Cant seem to find it. Have you got a link ?

Cheers

 

[flameport]

The part number is actually V4044F1000, digit missing from the previous post.

Documents for it here: http://europe.hbc.honeywell.com/products/ecatdata/pdf_v4044cf113_v4044f1000.html

No online suppliers, however this is not a commonly used item so would probably have to be specially ordered. The specification sheet has an error in it, the wiring diagram shows the 6 wires, but the table with ordering information has it described as a SPST switch which would only be 5 wires. You need the 6 wire version, so check carefully before purchasing.