Thermostat puzzle?

[Burnerman]

I've fitted a Drayton RTS room stat to my Worcester 12/14 Heatslave oil boiler.
I've wired it 3 wire, but I've noticed that the contacts inside the stat are arcing when closing (not every time)....in fact this morning the heating didn't come on, presumably because of this arcing.
I assumed my boiler wouldn't take more than 2 amps, but just in case I've reconnected it to a 2 wire system, without the neutral. Here it should be capable of switching up to 6 amps.
Could anyone please comment? With the 2 wire system the stat does work, but its hysteresis seems compromised.
Cheers!
John

 

[picasso]

I just googled drayton rts and its coming up as an elecronic stat ie needs live and neutral to work, have I got the wrong one ?

 

[Burnerman]

My apologies its an RTS8, the basic mechanical one
I'm using this after having a poor show with a wireless type.....anyway, it can be wired either 2 or 3, and really I'm wondering how much current the 12/14 conducts through its PCB connection (2 wire).
Its worked fine for a month but this morning failed.....buzzing, found to be the contacts arcing!
When wired as a 2, it does work but the hysteresis seems to be 2 degrees either side of its setting!
Thanks for the reply!
John

 

[ianmcd]

the third wire (neutral) is for the heat Anticipator its there to "smooth" out the switching of your room thermostat and prevent it from being erratic

 

[Burnerman]

Ok, I do understand the principle of heat anticipation - but my problem is, the stat didn't turn the heating on this morning!
Turning the stat to and fro a couple of times sorted that......I just want to prevent this in the future.
The arcing across the contact points was more than I would have expected.
John

 

[picasso]

Just looked at the instructions and they ask for a 5 amp fuse so it might be worth sticking a clamp meter on the stat to see what the boiler is pulling.

 

[Burnerman]

Aye, I think that has to be my next move.....I can't find any info on that one!
I just haven't any gear where I am at the moment......no worries, I can live with it!
Cheers
John

 

[ianmcd]

Ok, I do understand the principle of heat anticipation - but my problem is, the stat didn't turn the heating on this morning!
Turning the stat to and fro a couple of times sorted that......I just want to prevent this in the future.
The arcing across the contact points was more than I would have expected.
John

Really sorry John I have edited my response earlier, didnt look at the user name and didnt realise it was an experienced engineer asking the question thought it was someone with too much time on their hands looking into something they didnt need to look into, cant see why the anticipator being connected or not would make any difference on the actual switching of the stat, possibly I would bridge the stat out and see if you still have problems it may be an external wiring or the stat itself that is faulty

 

[Burnerman]

Hey no worries Ian - I'm just a bit out of my depth with this one so plodding on.
I reckon if I can find a stat that will switch 6 amps (with a neutral anticipator) I'm on to a winner!
Cheers
John

 

[denso13]

10 amps one which requires a neutral? http://www.tlc-direct.co.uk/Product...m+thermostat&gclid=CPT1zb_Ki7QCFQ7LtAod4yIAqw

 

[Burnerman]

Many thanks for that, denso - it could just sort things here.
The stat did work this morning, but the hysteresis is well out......the stat is set at 15, the temperature is 18 and the boiler is still on!
John

 

[matt1e]

Many thanks for that, denso - it could just sort things here.
The stat did work this morning, but the hysteresis is well out......the stat is set at 15, the temperature is 18 and the boiler is still on!
John

How have you wired the stat John is the switch live connected to 2 or 3?
You will need to measure the current to be sure but if its pulling more than 0.6 of an amp then you need to use L and 3 for 2 wire operation
if less than 0.6A then use L and 2 ( of course if this is the case then you shouldn't have any issues using 3 wire)
Incidentally your boiler will use less than the internal 3.15A fuse fitted but I would agree with you that it will no more than 2A at a guess

Matt

 

[Burnerman]

Hi Matt
Sorry for the late reply...been having dongle trouble
So - initially I went for 2A switching, boiler stat N to 3 and boiler stat L to L.
The neutral came from a spare in the PCB.
It seemed to work fine, but after a month (irregular use) this arcing started and at one time prevented the heating from coming on.
So, out came the spare neutral (The theory is now the stat can switch up to 6A). The arcing seems to have packed in - just the hysteresis isn't so good now.
I'm probably just being a B.O.F about it
Thanks for the reply!
John