Vaillant combi store cylinder stat problem

[robd]

Evening all,

A job I am on as an aside the customer asked me to have a look at the heating/hot water system as the hot water is not heating up. It is an unvented system with vaillant boiler and combistore cylinder.

Anyway I tested up to the tank stat/cylinder control and found power up to it (terminal 1) but not going through it out to terminal 2 or terminal 3 if I turned the temperature down. So I've called vaillant to check I'm not being daft (always a good chance) and they say no the stat is faulty you need a new one.

Long story short the customer ordered a new stat, I replaced only to find the same problem, I scatched my head and rang vaillant again and they said that's unlucky you must have a 2nd faulty stat....got another one sent and same problem again.

Anyway I bypassed the stat and had the system running fine. Bit of a head banger, have tested across terminals 1, 2 and 3 but nothing. Any thoughts welcome!

 

[Corbs]

any thermal cut out device on the stat that's tripped? other thank that you have bypassed the stat and the boiler and the motorized valve has opened so the wiring's ok so looks like you have another faulty or wrong stat

 

[Megavolt]

Is there a high limit stat your not seeing that needs resetting

 

[robd]

What a pipe stat? There is one I'll check it again when I go back next but don't think it's that, the cylinder control has 240v coming in but no going across, the pipe stat is above the cylinder and not directly connected so don't see that it could affect that.

 

[Corbs]

maybe a silly one but hay have you set the temp right should be around 60-65 dc

 

[robd]

Yeah had it right round doesn't switch over regardless

 

[davesparks]

What a pipe stat? There is one I'll check it again when I go back next but don't think it's that, the cylinder control has 240v coming in but no going across, the pipe stat is above the cylinder and not directly connected so don't see that it could affect that.

No, the high limit stat in the unvented cylinder controls, also known as a safety cutout.

 

[Meggerman]

Well, if you have the stat in your hand, turned down and no continuity across NC contacts then that's your problem still. You have already proved system by linking out (assuming you linked out at stat position).

 

[robd]

Sorry I see what you mean...possibly, would that be somewhere on the cylinder as opposed to being integral to the part that I've changed then?

 

[robd]

Well, if you have the stat in your hand, turned down and no continuity across NC contacts then that's your problem still. You have already proved system by linking out (assuming you linked out at stat position).

Yes mate linked across terminals.

 

[robd]

Could get continuity across spade bits on back but not on terminals on front, with stat turned up or down across either nc or no terminals

 

[Meggerman]

Yes mate linked across terminals.

Well if system ran when you did that then high limit safety stat must be closed also.

 

[robd]

It wouldn't run through the high limit stat between incoming and outgoing of stat then?

 

[Meggerman]

Could get continuity across spade bits on back but not on terminals on front, with stat turned up or down across either nc or no terminals

Are you sure there is no integrated high limit reset in that stat? As you should obviously have continuity between screw terminals and spades.

 

[robd]

There's nothing re-settable that I can see no

 

[davesparks]

I've never worked on one of these before but that looks like a reset button in the middle of the big shiny nut!

Are you sure you are experienced enough to be able to work on these? unvented cylinders can be pretty dangerous things if you were to do something silly like bypass a safety stat and let them get too hot! And of course they do have their own rules and regulations surrounding them.

 

[robd]

I've never worked on one of these before but that looks like a reset button in the middle of the big shiny nut!

Are you sure you are experienced enough to be able to work on these? unvented cylinders can be pretty dangerous things if you were to do something silly like bypass a safety stat and let them get too hot! And of course they do have their own rules and regulations surrounding them.

1. Yeah I was wondering if that was a re-set when I relooked at pic
2. If it is I find it strange if it needs re-setting when it is a brand new part
3. Don't worry I won't be bypassing the stat, I just did it to check I wasn't going (totally) mad and see the system would run
4. Yes reasonable amount of experience cheers but not afraid to look silly if I'm wrong, hence the post on here, by no means a heating system specialist though
5. If that is a re-set button and I've been on the phone to vaillant technical and they haven't mentioned to try it...oh never mind

 

[uksparks]

I don't touch heating, pipes, stats, trvs, anything that involves plumbing or central heating, ts a plumbers job, not mine, I don't have a clew what I'm doing. I'll be open and honest, I have no experience of heating controls.

 

[davesparks]

So you are posting here just to boost your post count then?

If you are an electrician then wiring heating systems is part of your job.
Unfortunately there are far too many people working in the domestic sector and calling themselves electricians that just can't wire boilers, it's ridiculous.
And then there's the ones who think they can but get it completely wrong when faced with 2 heating zones!

 

[Meggerman]

I don't touch heating, pipes, stats, trvs, anything that involves plumbing or central heating, ts a plumbers job, not mine, I don't have a clew what I'm doing. I'll be open and honest, I have no experience of heating controls.

It's not the plumbers job to wire and connect the controls, it is yours. What would you do on a new house that you were wiring if plumber said Im installing upstairs and downstairs heating zones and an unvented cylinder (S Plan +), would you sub it out?