NIBE Fighter 360P boiler / heat pump help needed

[ProDave]

Called to look at several jobs in one house today.

One is the electric heating system. It's an electric boiler combined with a heat exchange ventilation system and hot water tank. The users manual for it is here http://www.nibeonline.com/pdf/411483-1.pdf

The problem is the 40A MCB feeding it is tripping every other day. It used to be every few weeks, but it's got progressively worse.

I tried measuring the power it was drawing buy my b****y clamp meter seems to have packed up and was telling me just 2 amps.

I could really do with the installers manual for this.

All I have been able to determine so far is you can adjust the heat input between 7.5KW and 13KW If it's set to 13KW then it's no wonder a 40A MCB is tripping. So I want to find out how you adjust that. I suspect it's wire links or jumpers inside the unit.

Before my next visit I'll check out / repair / replace my clamp meter so I can actually measure what power it's drawing.

This one is yet another example of what to me seems unnecessarily expensive heating. Why would anyone choose to install an electric boiler like this, to drive wet under floor heating, and NOT even put the property on E7 or E10 tariff ?

As I keep saying if you are going to heat your home entirely by electricity, I would have though electric heating mats in this case to give electric under floor heating would be better.

 

[ProDave]

I've found the answer to my own question.

Further searching of the NIBE website allows you to search for the installation manual and eventually I found it (once you tick the box for obsolete models)

The heat input is set by a switch on the "monitor" panel and can be set for 3, 6, 7.5, 9, 10.5 or 13.5 KW

So should be a simple job to set it for the correct power input to match a 40A MCB and check it with a working clamp meter.

 

[batty]

I think they are quite a good system after changing one a few years back but as you say E10 probably would make them more efficient. The one i helped fit seemed to heat water up very quickly so you don't get the waste that you do with storage heaters.

 

[ProDave]

Well I went back today.

Nothing is quite as you expect. I had expected a "switch" so set the power levels, and assumed it used relays and a combination or series and parallel of a number of heating elements to set the power level.

Wrong.

The "switch" is in fact a potentiometer. So I assume all elements are in parallel, and it's either burst firing, or phase angle control that determines the power level.

So whichever it is, the peak current will be around 58 amps (13.5 KW) and it's only the average power level that will be set by this pot.

So that might explain why my digital clamp meter didn't like it.

Unfortunately I couldn't make any measurements today (I had my analogue clamp meter) because the whole house was toasty warm an nothing was calling for heat.

So I've turned it down a notch, and told him to call me if it trips again, and also asked if it does trip, leave it off for the house to go cold, so it will be calling for heat when I turn it on next time.

If my guess at 13.5KW peak and either burst or PWM firing of the heaters is correct, how would you expect a 40A type B MCB to behave?