Controlling DHW temperature with Worcester 30CDi

[splosh]

Hi everyone
I have just had a Worcester 30CDi system boiler installed in conjunction with a Megaflow 125 cylinder. The central heating is controlled with a DT10RF room thermostat and the hot water by a timer fitted within the main body of the boiler.

I am trying to find out if there is a way of controlling the temperature of the hot water using the Megaflow's built in thermostat. The Megaflow is currrently connected to the boiler by a temperature sensor which I gather is required by law to ensure the megaflow doesn't overheat. But this doesn't allow me to control the temperature of the hot water.

Does anyone know if there is another connection on the boiler that can be used for this or suggest another solution. There is of course the hot water control knob on the boiler, but even down very low, it still produces hot water at 75 degrees C.

Thank you

Roger

 

[bengasman]

Either you are doing something wrong or explained it wrong. To get dhw of 75 C, your boiler has to run for quite a while and at the very max. either your cylinder stat is not working of the immersion heater is on

 

[splosh]

Thanks for your reply Bengasman.

Maybe I didn't explain right. The immersion heater is not yet connected and the cylinder stat (next to it on the Megaflow) is also not connected to anything. The only connection to the boiler is via a temperature sensor / probe that came with the boiler and which is attached to the wall of the cylinder where the optional second immersion heater can be inserted.

I was trying to find out whether there is a way of wiring this cylinder stat up to the boiler in addition to the probe. I'm not sure whether these boilers have that facility.

 

[bengasman]

I am no expert on cylinders, but as far as I know a cyl stat is a cyl stat. Unless you have a dual coil. Second immersion heater? The only way to control you boiler is to connect proper cylinder stat to the wiring centre. If your installer did not do that, I would question his workmanship. It is one thing to leave a boiler to be switched manually for a day to avoid the client sitting in the cold, yet another to just leave it like that. Unless I misunderstood, and the sensor you mentioned is the actual cylinder stat. 65 C is a nice average temp for the cylinder. It is warm enough and prevents the necessity of the boiler running unnecessarily high. The boiler stat should be set no higher than needed to keep things warm, about 70 C. the cylinder stat will now prevent 2 things, waste of gas and stopping the boiler from cycling.
Another thing with cylinders systems is to make sure the heating and dhw are always on at different times. This will make the response much quicker.
Not overly important in your case as your installer misconfigured the system; either your boiler is twice as big as was needed, or your cylinder is too small.

 

[twgas]

if you have a megaflow it should be connected to a spring return 2 port valve wired through the cyl stat supplied with it as that has overheat protection built in

was the installer certificated to work on unvented

 

[gas4you]

Open the grey panel door on the megaflo and you will see a cyl stat that can be adjusted. Set this for 60C.

Be careful, or turn off power first as there are live wires in here as well.