WB 28CDi Compact with FW100 controller - flow temperature

[wiggers]

I've just had this system fitted and the last couple of days have been using it as the weather has turned a bit cooler. I've noticed the rooms take a while to warm up, longer than I was expecting and I've been looking at what the controller is doing.

It has set the desired flow temperature according to the outside temp and this more or less agrees with the curve for radiators in the manual. (10deg outside, 38deg flow temp.)

HOWEVER, when I watch the actual flow temperature on the info screen, it spends most if its time well below this desired temperature, in the low 30s. Occasionally it goes up to 42deg or so and then immediately starts dropping.

Is this normal or is there a problem somewhere?

 

[ALEC1]

my first instinct is the heating curve what is this set at?

 

[wiggers]

Sorry, I don't understand the question! The only curve I know about is the one printed in the manual relating outside temperature to flow temperature. It is set for radiators and as far as I know it can't be changed. The figures I've seen on the info screen show it is following the curve. The problem is the actual flow temperatures are much lower than the target ones.

 

[ALEC1]

p 56 of the manual..

heating curves do have something to do with radiators but there is no setting just for radiators, they may big or small which is why you get multiple curves.

have a look at the manual p 56

 

[wiggers]

On p56 it lists four Heating Circuit Types, one of which is Radiators and the corresponding curve is shown in Fig. 22. That is what the system is set to. I'm still not sure what you mean, sorry to be thick, this is my first system!

 

[ALEC1]

Also you dont say if you find the house warm enough or not..

if the house is warm, I would fret not... you can drive yourself mad trying to understand these things..but if you are comfortable why bother?

 

[wiggers]

I said the issue was that the house takes longer than I expected to warm up. Also, the bathroom with the TRV on 4 doesn't warm up as much as other rooms on 3.

What I want to know is why the flow temperature is significantly lower than the target temperature.

 

[ALEC1]

Is the system on long enough?

weather comp is really about maintaining two or more time windows of stable temperatures. It is not about heating places up rapidly like cave men used to light fires when they were cold..

If the FW 100 is on a wall as opposed to in the boiler, and assuming it can compensate the flow temperature it is probably lowering this to avoid over heating which causes discomfort.

 

[ALEC1]

the system needs balancing to resolve the issue of the radiator different heat out put

 

[wiggers]

Is the system on long enough?

The FW100 is in the hallway and I've closed the valve to half a turn on the radiator that is some distance away. Looking at the room temperature there it never reaches the desired temperature so I guess it is running the whole time. Even during warm weather when the plumber was testing, the room temperature went above the desired temperature but it continued to run.

I'll try reducing the lockshield valve setting on the rads that warm up first see if that makes a difference.

 

[wiggers]

the system needs balancing to resolve the issue of the radiator different heat out put

Is this the approved method?

http://www.homebuilding.co.uk/advice/DIY/how-balance-radiators

They talk about a 12deg difference between in and out, but if the FW100 is varying the flow temperature according to outside condition, then it will be difficult to get the 12deg drop when it is warmish outside. Presumably that 12deg refers to when the heating it running at maximum flow temperature?

 

[ALEC1]

I suspect the heating curve is set too high!

the room controller probably influences the flow temp (which is why the actual temperature is less than the demanded temp) but doesn't necessarily turn the boiler off..

so if the curve is too high then it will only reduce it a bit and you get over shoot.

have you tried calling worcester bosch?