Boiler wiring

[studentspark]

Boiler controls are an area where I have little experience, but I am working on it.

Boiler for pool and underfloor heating. Plumber is being called back but I am interested in whats wrong.

Boiler is getting no call for heat

stat sends signal for underfloor heat (hotwater pipes not electric)

This is the stat
View media item 41985
This is the boiler and controls

View media item 41984
looks like it used a CPC as conductor. 6th connector block grey switch live and Green and yellow in same block. green yellow goes to the LAE thermostat

Power is on the grey from the timer by the boiler when I manually switch this on
Nothing happens to this grey switch live from the room stat, it does not power it up.

The boiler is in standby mode and will not fire up.
It looks to me like the switch live is not going to the boiler.

Any thoughts

As I say I am not repairing this, using this to learn from.

Thanks

 

[ericmark]

One would guess it did work once? But I have found a whole estate where some one had used three core flex to wire up the cylinder thermostat using the green/yellow wire as a live wire connected to N/O contacts.

Central heating has so many plans each with it's own problems to list possible causes of faults would result in a very long list. Some of the problems can be quite elusive for example.

Most closed system boilers have a reservoir inside the boiler to allow for expansion as the water heats up. Looks like a ball with one water connection and a car tire valve. These are normally big enough for a standard system but with underfloor heating there is more able to expand so as the water heats up it the pressure release valve will open and dump the excess water.
As it cools the press drops as there is not enough water in the system. Boilers deal with this is different ways. Some will stop as soon as pressure drops and some measure flow and will continue to work the anti-vacuum device allowing air into the system.
In some cases the radiators can then act just like the expansion ball allowing the top of the radiators to fill with air. However the user then complains that the top of radiator is cold.

Where motorised valves are used this also causes a problem. One does not want the boiler to start until the valve is in the right position so instead of the thermostat acting directly on the boiler it works the motorised valve which in turn then turns on the boiler. So if the valve sticks then boiler will not fire up. Also of course if the micro switches inside the valve fail also the boiler will not fire up.

As a result often it's not a wiring fault but one little micro switch which stops it all working. However when you look at the plan for the motorised valve it will often show a single micro switch. But when you open the valve you may find three micro switches. It seems they also use micro switches to internally position the valve. So following the wiring diagram does not work as one gets some really odd readings due to the switches not shown on the diagram.

 

[bhm1712]

who on earth wired up that junction box? its a right shoddy mess.

 

[holmslaw]

..

 

[SUNRAY]

who on earth wired up that junction box? its a right shoddy mess.

And, by my interpretation, does not conform to current regs.

 

[bhm1712]

yep i agree...at the very least it has stranded and solid core cable mixed in the terminals of a JB

 

[Robin0577]

who on earth wired up that junction box? its a right shoddy mess.

And, by my interpretation, does not conform to current regs.

Agreed on both counts, but sadly it looks pretty damn good compared with most of the heating JBs I've seen in the past!

 

[JohnW2]

Agreed on both counts, but sadly it looks pretty damn good compared with most of the heating JBs I've seen in the past!

You just beat me to it! Anyone who thinks that's very bad clearly hasn't lived; even with my very limited exposure to such things, I've seen far worse!

Kind Regards, John.

 

[SUNRAY]

Agreed on both counts, but sadly it looks pretty damn good compared with most of the heating JBs I've seen in the past!

You just beat me to it! Anyone who thinks that's very bad clearly hasn't lived; even with my very limited exposure to such things, I've seen far worse!

Kind Regards, John.

Good heavens yes.
There is a site I have been on a number of times in the past & am waiting to get back to to take a pic, the boiler wiring and lighting circuit in a mass of choc block in the loft with no enclosure.

 

[bhm1712]

Agreed on both counts, but sadly it looks pretty damn good compared with most of the heating JBs I've seen in the past!

You just beat me to it! Anyone who thinks that's very bad clearly hasn't lived; even with my very limited exposure to such things, I've seen far worse!

Kind Regards, John.

This maybe (and IS because i have seen it myself too) the case, but it doesnt make it right for the person who installed it to say, oh well its against regs, its a mess but f**k it, its much better than usual central heating JB's out there so ill leave it...

 

[JohnW2]

This maybe (and IS because i have seen it myself too) the case, but it doesnt make it right for the person who installed it to say, oh well its against regs, its a mess but f**k it, its much better than usual central heating JB's out there so ill leave it...

Agreed, but I don't think anyone has suggested that.

With some attention to strain relief, IP status of the top and separation of solid and stranded conductors, I think I'd happily live with it. I'd personally like it to be a bit neater, too, but that's not really a significant safety or regs issue.

Kind Regards, John.

 

[ericmark]

I would agree wiring not the best and not the worst and will not comply.
However that was not the question.

I will admit I was also some what lost the first time I found a domestic central heating system. Up to then on commercial I had always had some sort of plan.

One of the problems was although Honeywell and the like made junction boxes with well defined connection criteria many electrical firms would try saving a few shillings by using socket backing boxes and lids as junction boxes with just connector strip inside.

If the Honeywell diagram had two line feeds in same junction box they would further try saving a few pence by combining them. As to diagrams you can forget them.

So when we go to a house first job is to try and work out what system has been loosely followed. But not only did the electricians cut corners also the plumbers did the same so one is faced not only with electrical uncertainties but also plumbing ones as well.

Underfloor heating can mean far more pipes to expand and contract to normal and pool heating can really upset the apple cart with so many methods used to transfer the heat. It also seems heat exchangers have many different names for example hot coil.

So the fact we can see a pressure gauge will point to a closed system i.e. no header tank. This may in turn mean there are a host of safety features designed to stop all sorts of problems including a holed expansion chambers.

So step one is to try and work out what system has been fitted.
Step two is talk to the people living in the house. What you need to work out is did it ever work correctly? One would be surprised at how many times systems have never worked correct and one is looking for a non existent part failure as it was just simply never wired correct in first place.
One is also looking for history. I had one where I was told how the guy in the house was upset by the disorganised mess in the airing cupboard and tidied it all up. This lead me to find how in the past the motorised valve had failed. As a quick fix some one had latched the manual control on the motorised valve to the bleed position which had allowed the system to of sorts work. The guy tidying up had knocked this and it had returned to standard position at which point central heating would only work when hot water was also required.

Although the fault and quick fix resulted in the radiators getting hot in the summer when hot water was used the occupants were sure this was not the case. So one has to be a little flexible too.

So come on guys give the guy some pointers of what to look for which will stop it working. Never mind if it complies with regulations.

 

[JohnW2]

So come on guys give the guy some pointers of what to look for which will stop it working. Never mind if it complies with regulations.

Well said!

Kind Regards, John.

 

[Aragorn84]

Having seen and repaired a similar fault on my brothers boiler, my suggestion would be to check the motors and microswitches inside the Zone valves.

Typically the "Call" for heat doesnt actually goto to the boiler, instead the call is used to operate the appropriate motorised valve (CH or HW typically, but you could have more), and once the valve is open theres a small arm which presses a microswitch, which in turn sends a live to the boiler to turn it on.

So the fault can be that the motor itself has failed, which can be diagnosed by manually pushing the little arm over to the flow position and seeing if the boiler starts. It could also be the microswitch itself, such that even though the valve has motored open, the switch never sends the live to the boiler, which can be checked with a multimeter on the appropriate pins of the valve.

 

[EFLImpudence]

Or the valve could be physically stuck and not moving all the way or not at all.