horstmann hct2 tank stat

[sts51L]

Hi peeps,
After lurking on this site for years and reaping the benefit of your knowledge and experience (for which i am very grateful) the time has finally come to ask a specific question. Please be gently with me.

I am currently finishing off an extension and am in the process of wiring up my boiler. It is a weissman system boiler. I am currently having problems with a horstamnn tct2 tank stat. I am bench testing the stat with the mains live going to com, call going to a lamp and the other side of the lamp going back to mains neutral. So the tank stat is acting as a simple switch. The problem is when the switch is open i am still getting 60 volts across the lamp. The resistance across the stat is infinite in the open position and it is a new stat. Any ideas?.

 

[mikely]

Is the problem that the thermostat does not work when connected into your heating system, or that it does not turn on the lamp in your test rig, or just that you can’t explain why you should measure 60V across the lamp when power is not applied to it?

 

[sts51L]

Thank you for your reply. When the whole system was rigged up, timer ,room stat and tank stat, with two lamps to simulate the switched lives to the boiler the lamps came on when heat was called for. When the stats were switched off both lights went out but there was a slight glow from the tank stat lamp. I isolated the stat and wired it seperately as discribed above and still had the same issue. When switched off there was still a slight glow from the lamp indicating that there was still power passing through the switch and lamp. I have tried an old tank stat with the same result. I guess my question is is this normal?.

 

[matt1e]

cheap digital multmeters can give erroneous results like you describe due to their high impedance loading, but that would not explain the lamp glowing,
why are you using two lamps to simulate the boiler anyway? I think you would be better off posting a diagram of how you have wired your test rig.
have you wired in any valves etc

Matt

Ps what problems are you having with the stat, and what system plan are you trying to achieve?

 

[picasso]

Have you wired a three port valve in as well as the timer stat ect?

 

[sts51L]

Thanks for the replies. It's a four pipe (one heating circuit and one cylinder circuit) system boiler so the pump and diverter valve are in the boiler. Both "call for" signals (room stat and tank stat) are wired directly into the boiler. I don't know whether it's all the eggnog and quality street but i just can't understand why a stat which should be a simple switch should still allow power through in the open position.

 

[picasso]

Sure you got the polarity correct ? you would get that voltage if you were switching the neutral.

 

[matt1e]

Thanks for the replies. It's a four pipe (one heating circuit and one cylinder circuit) system boiler so the pump and diverter valve are in the boiler. Both "call for" signals (room stat and tank stat) are wired directly into the boiler. I don't know whether it's all the eggnog and quality street but i just can't understand why a stat which should be a simple switch should still allow power through in the open position.

It isn't allowing power through, its just that there is a potential difference between the contacts when the switch is open due to the internal boiler circuitry

Matt

 

[RF Lighting]

You might be better asking this on the electrics forum, as none of the plumbers seem to have a clue how electrics work.

Your stat is goosed. Nothing complicated about that at all.

 

[matt1e]

You might be better asking this on the electrics forum, as none of the plumbers seem to have a clue how electrics work.

Your stat is goosed. Nothing complicated about that at all.

Really?
I would read through the thread again carefully if I were you
Give me a shout if you need anything explaining

Matt

 

[matt1e]

Second thoughts, ignore me RF apologies it's me that should read through again and stay of the drink
I don't think it's the stat though
More the way the op has wired things,
A diagram of what he has done would help explain things though

Matt

 

[RF Lighting]

the mains live going to com, call going to a lamp and the other side of the lamp going back to mains neutral.

This is the most basic of basic electrical circuits. There is a resistive load on the circuit so it does not matter whether it is tested with a high or low impedence meter. If there's a voltage across the lamp the only place it's coming from is the stat.

Even if it was wired reverse polarity there wouldn't be a voltage across the lamp.

It's a faulty stat.

 

[doitall]

Feedback on the neutral.

 

[sts51L]

Thank you for all the replies. Hope everyone had a good one. I'm begining too think the ring main might be iffy. Although i've recently had a new CU fitted and everything seemed ok. There certainly seems to be something leaking back through the neutral.

 

[RF Lighting]

Feedback on the neutral.

It is NOT feedback on the neutral. If you had even a basic grasp of how electrical circuits work, you'd understand how this could NOT be the case.

It really is time you stopped giving out "advice" on electrical matters until you have an understanding about what you're advising about.

All you've managed to do is confuse the OP and lead him up completely the wrong path.