cyclinder stat blowing fuse

[Chrisel]

Called out by a plumber I do work for. He had recently installed a new zone valve and chaged CH/HW programmer. A fortnight later the customer calls him because he has lost all heating. Plumber turns up, realises 3A fuse has blown in switched fused spur. He can't change it without it blowing. Calls me.

The spur supplies the boiler which, as well as central heating, heats water into the tank. Spur therefore also supplies programmer, zone valve and cylinder stat. I identify the cylinder stat as the issue; we replace this. Everything starts up, we run the system. Everything is working well.

No. Two days later the customer calls the plumber, the fuse has blown again.

Before I return to the property and recover exactly the same ground, is there any advice out there as to what might be causing this. Could there be an underlying problem that I missed, causing a problem through the stat. I don't want to have to return every 2 days and install a new cylinder stat.

Thanks

 

[HandySparks]

Why did you think the cylinder stat was the problem? What tests did you do?

 

[stigwart]

You say the plumber installed the valve, did he do the wiring connections too?
Is it possible that the cylinder stat was temperature satisfied at time of replacement, but after you had gone the stat called for heat, there was a termination error at the wiring center, and pop??

 

[Chrisel]

Before I continue I will admit I did not carry out as thorough testing as I should have. I had just finished another job for him, just as I had packed up the van and was about to drive away "could you go and look at a problem for me..." I then had a very short window to get the job sorted out. Enough excuses....

When I started testing, nothing made sense at all, I couldn't identify any cables leaving the programmer and arriving at the junction box. I didn't want to start taking everything apart so I simply went through each step.

Disconnected the hot water side of the programmer: power stayed on. With HW ON channel disconnected everything stayed on.

Then disconnected each item on the HW side. The usual culprit I find is the pump but the fuse still blew with that attached. When I disconnected the cylinder stat the fault was removed. It was at this point I tested the cable I had disconnected at the programmer (blue) with the cable I had just disconnected (red) and realised there was a join somewhere. Indeed; on digging around I find another (hidden) junction box, which explains my initial problem with identifying cables when testing and making sense of how it had previously been wired.

We changed the stat, ran the hot water and central heating, everthing was okay.

In an ideal world I would probably return and rewire the whole thing so that there is only one 10-way junction box but we are not in an ideal world.

I was just enquiring as to whether people here have encountered a common problem with regard to cyclinder stats in order to at least give me a starting point when I return. I am quite prepared to put several hours aside on Monday to just start testing everything one by one but thought it doesn't hurt to have some advice in advance as my experience with these systems is limited

 

[Chrisel]

He did the wiring, yes. He assured me he just replaced like for like.

Anything is possible. The thing I keep coming back to is they used the system for two weeks after he made the initial changes so I find it unlikely (but admittedly not impossible) that him changing the valve caused the problem.

Similarly, it worked for two days after I was there. Having said that it has just occurred to me, they called him two days afterwards. That doesn't mean anything does it?

 

[MDJ]

He did the wiring, yes. He assured me he just replaced like for like.

Anything is possible. The thing I keep coming back to is they used the system for two weeks after he made the initial changes so I find it unlikely (but admittedly not impossible) that him changing the valve caused the problem.

Similarly, it worked for two days after I was there. Having said that it has just occurred to me, they called him two days afterwards. That doesn't mean anything does it?

you may as well let a Chimpanzee connect the system up then, lets face it, he has connected it up wrong, end of LOL

 

[GLENNSPARK]

what are we talking here s type?

s plan sorry..

 

[GLENNSPARK]

ok...its a zone valve yes....
so its s plan...
first check the salamander box...

you should have a supply..phase, neutral & CPC

from that you will have the supply going into the control....
it will be linked out in the back of that....3 and 5...i think...
you will have then a twin coming back out from the control wallplate and into the salamander box.....one core of this will go to the room stat....the other to the cylinder stat....then from there back to the salamander box and to the zone valves...
the zone valves require a neutral & CPC + a perminant live from the incoming twin....(use the grey for this)....the orange then goes to the boiler & pump

 

[Chrisel]

Y plan (with the mid-position zone valve?)

 

[HandySparks]

..first check the salamander box...

Eh? What's one of those?