Mid Position valver trips Circuit Breaker

[Derek Reay]

Hello,

I have been working on a Central heating system where , after selecting the heating to come on, it often trips the Circuit Breaker. Throughout the Summer, it appears that there were not any problems, when only the Hot Water was selected on the Timer programmer.

Both the valve and the Pump are situated in the loft as the property is a Bungalow. Having looked at the Mid position valve it seems that this had been a replacement for a 6 wire valve. I say this because there was a 'Switchmaster' controller , with cut off wires, next to the BGMVSP 23 valve. There was also another empty box next to that, but the label had faded.

Having looked quickly at the junction box, there is a 6 wired cable coming out, which is connected to a small 2 part, 5 terminal cable connector block. That part of the block has both a Red wire and also an Orange wire connected together in the same terminal. However, the cable from the actual valve is only a 5 wire cable. and each of these wires is connected to its own, individual terminal in that part of the connector block.

I am assuming that these different wires are causing the tripping of the Circuit Breaker, once the Heating is turned on.

Can anyone advise on this strange set up please. Or should I study all of the wires in the Junction box, and re-wire the valve into the box with just its own 5 wire Cable?

Many thanks,

 

[HandySparks]

...That part of the block has both a Red wire and also an Orange wire connected together in the same terminal. However, the cable from the actual valve is only a 5 wire cable. and each of these wires is connected to its own, individual terminal in that part of the connector block.

I am assuming that these different wires are causing the tripping of the Circuit Breaker, once the Heating is turned on.

Worth finding out when the valve was last changed. If this setup was working OK last winter, then the wiring configuration isn't going to be the fault.

 

[Lucien Nunes]

That wiring sounds correct, the red wire of the old valve was the output to boiler SL (new valve orange) which is now tied to the HW-on from programmer (old valve orange). I.e. it sounds like you have a genuine fault. What trips - MCB or RCD?

 

[Derek Reay]

That wiring sounds correct, the red wire of the old valve was the output to boiler SL (new valve orange) which is now tied to the HW-on from programmer (old valve orange). I.e. it sounds like you have a genuine fault. What trips - MCB or RCD?

Hello again,

Regarding the turning on of the Heating, which trips the Consumer Unit, it was the RCD that had just tripped.

The new owner of the Bungalow only moved in last year. However there was some paperwork handed over which showed that the Central Heating system had been serviced annually. It was noted that a C/H engineer had also been called out, on at least a couple of occasions as well. It would appear that the Mid Position Valve had been changed at least 3 years ago.

Last year, when the new owner turned on the Central Heating it tripped the Consumer Unit. A 'Corgi' registered engineer was called out, and he was at the Bungalow for a couple of hours.
He apparently tried different actions on both the Water, and the Heating thermostats, tried all the controls on the Programmer and also looked at the Electrical Junction box in the Loft. He did manage to get the heating to come on for a few minutes, but then the Consumer Unit tripped itself again. He attempted this a couple of times, then eventually managed to keep the system from tripping out.

He did advise the owner that although he was a Central Heating engineer, he was not an electrician. As such, although he could look at the wiring on the Thermostats, the valve and the pump, he was not qualified to test/rewire the Electrical connection box. As the Heating stayed on throughout the cold period it was only turned off when the weather warmed up.

The heating was only turned on again last week, when it immediately tripped the C/U.

The programmer is an old Switchmaster unit, with push button controls, and the Electrical box is an unknown make small box. The Heating is still turned off and the Hot water, which is on the timer is working fine.

I wonder whether it would be beneficial to renew both the programmer, and the Electrical connection box, and possibly the wiring between them, and use just the 5 wires from the valve.

Any advice on this problem would be appreciated.

Many thanks.

 

[Lucien Nunes]

Are you an electrician?

Any fault that trips an RCD is likely to be traceable with IR tests. In a system such as this, with basic non-electronic controls, most of it can be tested (with the general exception of boiler PCBs) without the test causing damage. I would identify points in the circuit that are energised only in the state in which the trips were known to occur and test them to CPC, as a first step. There might be some evidence already that the tripping only happened when the room stat was in CFH or once the valve had opened, which narrows it down quite a lot. As it seemed not to have tripped through much of the winter, look for cables / connections that might be affected by heat or damp.

You spoke of 'room stats' in the plural. If these are traditional bimetal stats and the installer sneakily ran the accelerator resistors to CPC instead of N, their total additional leakage might push an RCD over the edge whenever they all CFH. An IR test on the CH-on line will find this as well as a visual in the stats (or a lack of 3C+E in the JB!).

Finally, I doubt the programmer itself is at fault as this is probably double insulated, although the CPC is probably present as far as the backplate in which case a wiring fault or flashover between terminals there (which I have seen) is a possibility.

 

[Geordie Spark]

<<<< He did manage to get the heating to come on for a few minutes, but then the Consumer Unit tripped itself again. He attempted this a couple of times, then eventually managed to keep the system from tripping out.

He did advise the owner that although he was a Central Heating engineer, he was not an electrician. As such, although he could look at the wiring on the Thermostats, the valve and the pump, he was not qualified to test/rewire the Electrical connection box. As the Heating stayed on throughout the cold period it was only turned off when the weather warmed up.

The heating was only turned on again last week, when it immediately tripped the C/U. >>>>>>>>>>>

This is making me think there's a small leak somewhere which is shorting something out.

As long as the boiler is running and everything's nice and warm the water from the leak is evaporated before it can short- out anything, but when the heating has been off through the summer that leak has had free rein to cause whatever havoc it likes!!

I haven't read through all of this thread so don't know if this is a Combi boiler but suspect it isn't because there is talk about an "unknown make of electrical box" which tells me that this is a "System Boiler" with separate water tanks outside of the boiler casing (i.e. in the loft perhaps?) and maybe - just maybe - the seal on the diverter valve shaft has a very slight leak allowing a bit of moisture to get into the leccy bits of the motor.

Question: What is the orientation of the valve ...... is it mounted on a pipe which runs horizontally so the motorised head sits on top of it with the shaft running vertically down into the valve body or is this valve mounted on a pipe running vertically so that the shaft enters the valve in a horizontal direction?

My thinking is if the valve is mounted on a horizontally running pipe with the shaft running downwards then any moisture escaping between the shaft and its seal should not get high enough up to get near any sparky bits, but if the valve is mounted on a vertical running pipe it can - and will.

 

[Silly Sausage]

<<<< He did manage to get the heating to come on for a few minutes, but then the Consumer Unit tripped itself again. He attempted this a couple of times, then eventually managed to keep the system from tripping out.

He did advise the owner that although he was a Central Heating engineer, he was not an electrician. As such, although he could look at the wiring on the Thermostats, the valve and the pump, he was not qualified to test/rewire the Electrical connection box. As the Heating stayed on throughout the cold period it was only turned off when the ..............................................



on a pipe which runs horizontally so the motorised head sits on top of it with the shaft running vertically down into the valve body or is this valve mounted on a pipe running vertically so that the shaft enters the valve in a horizontal direction?

My thinking is if the valve is mounted on a horizontally running pipe with the shaft running downwards then any moisture escaping between the shaft and its seal should not get high enough up to get near any sparky bits, but if the valve is mounted on a vertical running pipe it can - and will.

Come on now Old Chap, electrics, water, lead, valves, taps... it's all too easy to get confused.

Here's the the right forum for you...

Plumbing Forum | Plumbing Advice | Plumbers Forums | A forum for plumbers advice in the UK

 

[Geordie Spark]

Come on now Old Chap, electrics, water, lead, valves, taps... it's all too easy to get confused.

Here's the the right forum for you...

Plumbing Forum | Plumbing Advice | Plumbers Forums | A forum for plumbers advice in the UK

I'm far to advanced to be mixing with that rabble!!

The main things that confuse me just now are hospital consultants who can't make-up their minds if they are going to stick a needle in my knee of chop a lump out of a vein in my neck and then at the end of it all tell me they can arrange for me to have a Social Worker, Hearing Aid and a Commode!!!!

 

[tidyboiler]

for Geordie

 

[itselectric]

If it trips calling for central heating, but works otherwise , the first thing I would be looking at is the pump. Especially if it has run alright during summer.

 

[davesparks]

If it trips calling for central heating, but works otherwise , the first thing I would be looking at is the pump. Especially if it has run alright during summer.

Why? Gravity systems are pretty rare these days, you'd normally assume fully pumped unless otherwise stated.

 

[Geordie Spark]

Why? Gravity systems are pretty rare these days, you'd normally assume fully pumped unless otherwise stated.

I've spent many happy hours converting gravity systems to fully-pumped and many more ripping them out & fitting Combis.

 

[davesparks]

I've spent many happy hours converting gravity systems to fully-pumped and many more ripping them out & fitting Combis.

I've wired many such conversion jobs,

 

[Derek Reay]

I've wired many such conversion jobs,

Hello again,
I'm afraid that I am still seeking advice regarding this C/H tripping the electrics.
I have now I.R. tested all of the wiring from the Consumer Unit to the wiring junction box, and all is ok.
At this moment in time I have not tested the Water and Central Heating stats, there are just 1 of each Nor the wiring to the Mid position valve, nor to the boiler or pump. It took quite a while to find out which wires went where, and also how they were all connected up.

I am not sure as to how to check the wiring to the M/P Valve, as I have been unable to find a wiring diagram which details what each wire is actually activating, or not activating.

As it is the RCB that has been tripping this would seem to be a major fault, but there is no evidence of any cables being burnt, broken or chewed.

I have noticed, however, that there is a wire connecting the Grey wire at the valve ( + terminal) to the Hot Water off terminal on the programmer. This wire, in turn is also linked to the H/W thermostat, and the Orange wire at the Pump, which in turn links to the Boiler.

All suggestions and advice are welcome.

Thank you,

 

[davesparks]

I'm afraid it might be time to call an electrician if you are out of your depth with this. Domestic central heating controls is a very basic thing which any electrician will be able to test through pretty quickly