Frost Stat not working

[flutterbye]

Hi

We have an S plan system installed by BG some years ago. The boiler is in the garage and the pump and valves in the airing cupboard.
The boiler is "protected" by a pipe stat and frost stat. Today I got a chance to test it. With the system was off at the programmer and stone cold, I went into the garage. For the first time, I heard an audible click on the frost stat when I rotated the dial. I believe that meant the pipe stat had got cold enough to power the frost stat which I assume is wired in series.

However, turning the frost stat up and hearing the click had no effect whatsoever on the boiler. (Nor the pump or valves for that matter). The rest of the heating and HW system is working fine.

Does this mean it is likely the frost stat has been wired incorrectly? Its a long way from the garage to the airing cupboard and so maybe BG simply didn't connect it up to the junction box in the airing cupboard? I wonder if it could just be wired directly to the boiler since there are no places colder in the house that the flow/return in the garage?

Thanks in advance for any thoughts/advice.

 

[namsag]

A frost stat is usually for boiler protection only.
So on an S plan it will not open either motorised valve it should be wired so that it brings the boiler and pump on which will put the heat around the bypass circuit untill the right amount of heat is there to satisfy the pipe stat or frost stat.


So basically a permenant live loop out of junction box into the frost stat
If cold enough the frost stat contacts will make.

Out of frost stat into pipe stat and back to the junction box connected to pump/boiler live which will also be attached to the lives out of the microswitches on moyorised valve(either grey or orange wires usually).

Once either the frost stat or pipe stat gets the correct temp to it to break call for heat(usually pipe stat) it will turn boiler and pump off, depending wether there is a pump overrun the pump may stay on for a while

 

[D_Hailsham]

For the first time, I heard an audible click on the frost stat when I rotated the dial. I believe that meant the pipe stat had got cold enough to power the frost stat which I assume is wired in series.

Yes they are in series

However, turning the frost stat up and hearing the click had no effect whatsoever on the boiler.

You have to turn the frost stat down to turn the boiler on. It works the opposite way round to a room thermostat.

Honeywell (Wiring Guide issue 16) show the frost protection connected to the brown wire of one of the valves for S plans. This will open the valve so the boiler lights via the microswitch.

 

[mysteryman]

It works the same way as a room thermostat, but at a lower temperature and bypassing the timer. On with falling temperature; off with rising temp.

 

[D_Hailsham]

It works the same way as a room thermostat, but at a lower temperature and bypassing the timer. On with falling temperature; off with rising temp.

My head hurts!

 

[flutterbye]

Thanks for the replies.

I was assuming that the fact that I could hear the frost stat click for the first time meant that the pipe stat had been triggered but perhaps that is rubbish and in fact even though they are "wired in series" they both have power all the time and me be able to get it to click was simply because the temperature was below 10 degrees which is the maximum temp of the stat ?

SO in other words, maybe nothing is wrong, the frost stat could be satisfied but the pipe stat was not which is why nothing happened either side of the frost stat click?