Where to place a thermostat on HW cylinder

rhonin

We recently had a 250L triple coil hot water cylinder installed. It has a thermostat on it that is connected to motorised valves. Its set to 60C. The problem is that I think its placed too low down in the cylinder. Its not that far up from the bottom of the cylinder. As a result the motorised valve doesn't close because the temperature isn't reaching the temperature set on the thermostat.
Where is the best place to put the thermostat?

Pete67

Approx 1/3rd of the way up from the bottom is the usual recommendation.

freddyuk

Reduce the temperature setting on the thermostat until you get the desired outlet temperature? Save a lot of messing about.

rhonin

Seems the bottom third of the tank stays cold for some reason. Top part is roasting. Rads are roasting too so not sure why the rest of the tank isn't heating .

freddyuk

What are the other coils connected to? Bottom would normally be solar so there should be 1 or maybe 2 sensors to control this and then maybe a wood burning stove or similar and the top coil for your main boiler. So if it is your main boiler circuit for DHW then fit the stat nearer the coil for that circuit as you would be using water in the top part of the cylinder for DHW. We need to know what other heating sources you have as they need to work in harmony and each one will be controlled by a thermostat/sensor.

rhonin

freddyuk wrote: »

What are the other coils connected to? Bottom would normally be solar so there should be 1 or maybe 2 sensors to control this and then maybe a wood burning stove or similar and the top coil for your main boiler. So if it is your main boiler circuit for DHW then fit the stat nearer the coil for that circuit as you would be using water in the top part of the cylinder for DHW. We need to know what other heating sources you have as they need to work in harmony and each one will be controlled by a thermostat/sensor.

There are two input pipes at the top of the tank each with a motorised valve. One is coming from the back boiler and the other from the oil boiler. The bottom coil isn't connected yet but will be connected to solar panels next year. The current main source of heat is from the back boiler with oil as backup.

Carlow52

rhonin wrote: »

There are two input pipes at the top of the tank each with a motorised valve. One is coming from the back boiler and the other from the oil boiler. The bottom coil isn't connected yet but will be connected to solar panels next year. The current main source of heat is from the back boiler with oil as backup.

What order are they in, starting from top
Oil
BB
Solar
or
BB
oil
Solar

rhonin

Carlow52 wrote: »

What order are they in, starting from top
Oil
BB
Solar
or
BB
oil
Solar

The oil and back boiler are connected at the same level but on either side of the tank. The back boiler comes in from the left and the oil from the right but on the same height.
Solar is at the bottom.

Carlow52

Thanks for that.
Now are u saying that the BB loop has a motorised valve on it so as to cut off the loop once tank stat cuts out?

If so what happens the heat from back boiler then?
I presume the BB loop is an open system with heat dump etc

Is the oil system open or closed?

DoneDL

Pete67 wrote: »

Approx 1/3rd of the way up from the bottom is the usual recommendation.

I was always told that 1/3 way up the cylinder was correct but the Danfoss WP 75 recommends 1/2 way up. So I would say manufacturers instructions or 1/3 up:)

rhonin

Carlow52 wrote: »

Thanks for that.
Now are u saying that the BB loop has a motorised valve on it so as to cut off the loop once tank stat cuts out?

If so what happens the heat from back boiler then?
I presume the BB loop is an open system with heat dump etc

Is the oil system open or closed?

Yeah the motorised valve on both BB and oil is supposed to close when thermostat on HW cylinder reaches 60C. Once closed the hot water goes to radiators only. The area on the tank where the thermostat is currently located it doesn't heat up so the valve remains open.
I suppose my queries are, is the thermostat located too low in the tank and if not why doesn't that area of the tank heat up.

DoneDL

The tank will not fully heat up unless the lower connections on the cylinder are used. That two port on the BB connection better be a Honeywell 4043B or similar.

rhonin

DoneDL wrote: »

The tank will not fully heat up unless the lower connections on the cylinder are used. That two port on the BB connection better be a Honeywell 4043B or similar.

Ok that makes sense why it doesn't heat fully heat up so the thermostst should really be moved up.
The two port is a Myson Power extra.

DoneDL

I would not fit a valve to the primary pipework of a solid fuel system. The honeywell valve is sprung open so in the event of a power failure the valve will stay open but I don`t like relying on a valve that is mechanical and could fail. I would remove the valve entirely.

Carlow52

OP are u 100% au fait with the concerns being alluded to here re MV's on the BB circuit?

rhonin

Carlow52 wrote: »

OP are u 100% au fait with the concerns being alluded to here re MV's on the BB circuit?

I am. I will be chatting to the plumber about changing the MV valve.