Ideal Vogue System hot water flow temp

[jonw]

Hi experts, I have a Ideal Vogue system conventional boiler 26kW, plus megaflo (installed about 7 years ago). Recently I lowered the boiler central heating temp to 63 degrees down from much higher. The user manual calls this the central heating flow temp control. It lowered the temp of the flow to central heating as expected, but it also lowered the flow temp from boiler to the megaflo hw tank. It this right? The effect of this is that it takes much longer to heat the hw.
I just assumed that a central heating temp control would only change temp to rads and for hw the boiler would be controlled by megflo thermostat ( that the boiler would work hard to achieve hw temp and then let megaflo thermostat shut it off?) Am I missing something here, is there an installation error with my system or is that just how it works?
Any information would be appreciated, cheers Jon

 

[JonathanM]

Normally, that is just how it works. In most cases, the boiler is only set up to provide one flow temperature, which is the same whether it is heating the radiators or the hot water cylinder.

With most boilers these days, though, there is an option to set up the system so that the hot water cylinder actually does heat at a higher flow temperature. It's called priority hot water, or PDHW. But it would almost certainly involve fitting a different motorised valve and some rewiring of the boiler. The video below shows an Ideal Vogue being set up for PDHW. I don't know if yours can do this as there has been more than one series of Ideal Vogue.

 

[jonw]

Thanks JonathanM. That's what I wanted to know. The video is good, very informative. Although slightly different to the boiler in the video (mines probably older) my boiler does appear to have seperate switched lives for HW and CH. Its good to know it might be a possibility- I'll check with the plumber next service.

 

[JonathanM]

Its good to know it might be a possibility- I'll check with the plumber next service.

One thing to think about is that in most PDHW set ups, the central heating can't be on whilst the cylinder is heating. So, depending on how long your cylinder takes to heat up, there might be a concern about the house cooling down, when it's very cold outside. Modern cylinders like yours should heat very quickly though.

 

[jonw]

Yes, I noticed that in the video. Worth thinking a bit more about. I had fast recovery time before I lowered the temp from 75 degrees, in the order of 20-25 mins if the HW tank isnt completely cold ( say 25-30 deg). CH off for 25 mins would probably be ok in this house.

 

[RandomGrinch]

You may also need to consider the legionella risk of a lower tank temperature.
It's killed at 60C, but having a flow temp of only 63C may mean not all of the water in the tank reaches that critical temperature.