CH also heats DHW

[Ian Duggan]

Apologies if this is an already answered question, I did check the Wiki and the FAQ, but nothing quite lines up.

We've got an oil fired boiler (an ancient Camray 5) that has an integrated 12 litre hot water tank for DHW. The original system only had a Summer / Winter switch on it, no controls beyond that. But an optional timer was fitted to our one.

The part that's puzzling me is when the CH is running, and the hot water is set to "off", the DHW tank heats up as well. From what I can see in the diagrams in the manual, that should never be the case.

We did have to replace the actuator on the 3 way valve, as we were getting hot water but no heating at one point, but that appears to be working as intended now.

I guess what I'm unclear on is, is that expected behaviour on an oil-fired boiler with an integrated water tank, that having the CH on would also heat the DHW tank? Or is the 3-way valve not quite doing what it should i.e. going to CH only with no heating of the DHW.

With oil at the price it is, I don't really want to heat the DHW tank every time the CH is on...

 

[oldbuffer]

1. Check the 3 way valve is a diverter valve, and not a mid position valve.
2. Check the wiring between the programmer and the zone valve. The zone valve normally requires a "hot water off" signal from the programmer.

 

[oilhead]

Is your ancient Camray 5 with an 'integrated 12 lt Hot water tank' really a Camray 5 Combi? If so, it will always give priority to hot water. A picture would help.

 

[Ian Duggan]

Is your ancient Camray 5 with an 'integrated 12 lt Hot water tank' really a Camray 5 Combi? If so, it will always give priority to hot water. A picture would help.

I didn't know the exact model number, but yes looking at pictures online, it's a Camray 5 Combi 55 or 70, yes.

It's not that it's giving priority to the hot water, it's that it's heating the tank when the hot water is marked as off. Which seems like a waste of oil?

 

[Ian Duggan]

1. Check the 3 way valve is a diverter valve, and not a mid position valve.
2. Check the wiring between the programmer and the zone valve. The zone valve normally requires a "hot water off" signal from the programmer.

Thanks, the "hot water off" could be a good shout, I think I spotted a signal wire between the controller and the boiler that matches that, I wonder if that's not happy for some reason.

 

[oilhead]

You'd need to see how the programmer is wired to the boiler. You have the option of setting a lower temperature on the hot water stat. This will reduce the temperature of the slave tank, but you will have no hot water until you turn it up.