3 Nests, Boiler, Megaflo and UFH - wiring assistance

[LFletcher]

Hi,
I'm doing a refurb of my house and as part of that all of the old plumbing and electrics have been replaced (by their respective tradesmen).

In the new world order the downstairs heating is run off a 9 port polypipe ufh heating manifold and a new system boiler and megaflo have been placed in the loft.

The boiler and the megaflo each have their own dedicated radial circuits (and FCU's) running back to the consumer unit.
The ufh manifold is in a utility room which has it's own ring circuit and a FCU to power the pump and wiring centre.
The consumer unit is a Hager one populated with rcbo's.

When the heating engineer came to install the 3 nests (to control separate zones on the ufh and the water) we ran into issues.

Running the nests to control the manifold, pump, actuators, and the wiring centre downstairs all seemed to work fine.

The loft has it's own wiring centre for the boiler and megaflo (S plan circuit). Which also appears to work fine independently.

When connecting the 2 systems together - that's when the issues started.
When the connection to either the heating or water was triggered (from the nest) the rcbo's for both the utility room ring and the boiler would trip.

Initially he thought the cable between the loft and utility room might be the cause, but that was eliminated.
Ultimately he was unable to diagnose what the issue was on the day and is coming back this week to fix it.

I noticed that a neutral cable on one of the double sockets on the utility room ring was loose - could this have contributed to the rcbo's tripping when a heating or hot water call was made to the boiler?

It's also been suggested that the wiring centre in the loft and the one for the ufh manifold downstairs need to be powered by the same connection otherwise they will keep on tripping - does anyone know if this is correct and the way the system should be wired?

Thanks for your help

 

[SparkyChick]

Because the different systems are on different circuits, when they become interconnected, there will be an imbalance in the line and neutral that the RCBOs are picking up on resulting in the tripping.

The entire heating system should be run as a single circuit (that doesn't mean one long radial circuit necessarily, but all powered from the same protective device).

 

[LFletcher]

Thanks - very much appreciated.

The boiler is currently on a 16A rcbo.
Do you think I will need to get the sparky back to swap if for a 20A one if adding the ufh manifold onto the same radial?

 

[buzzlightyear]

The boiler is currently on a 16A rcbo.
Do you think I will need to get the sparky back to swap if for a 20A one if adding the ufh manifold onto the same radial?

no is the answer .has in post#2.the fuse to the boiler is 3amp via wiring centre.

 

[Leesparkykent]

Totally incorrect...all the heating controls should be fed from the load side of one switched fused spur. What you have is completely wrong and probably a major ball ache to put right.

 

[Octopus]

And you say respective tradesmen installed this shambles?

 

[Octopus]

Wonder why the boiler is on a 16A RCBO?

 

[buzzlightyear]

Wonder why the boiler is on a 16A RCBO?

may be the op can in light us.

 

[davesparks]

Wonder why the boiler is on a 16A RCBO?

It’s traditional to install a 2.5mm 16A radial to feed a boiler, and most domestic circuits these days need an RCD. It’s what I’d do if I was wiring it from scratch.

 

[Octopus]

It’s traditional to install a 2.5mm 16A radial to feed a boiler, and most domestic circuits these days need an RCD. It’s what I’d do if I was wiring it from scratch.

Sure a 16 a provides for flexibility in the future .....

 

[LFletcher]

Totally incorrect...all the heating controls should be fed from the load side of one switched fused spur. What you have is completely wrong and probably a major ball ache to put right.

As far as I can tell there are 2 x 3 core and earth (1mm) running from the wiring centre in the loft to the wiring centre by the ufh heating manifold. I assumed (incorrectly?) that this was to be used for control rather than control and power to the manifold/pump downstairs?

The one saving grace is that if it is wrong it's still possible to get a cable from the loft to the utility room if required.

 

[LFletcher]

And you say respective tradesmen installed this shambles?

Yes, builder provided plumber and electrician. Neither knew how to get multiple Nest thermostats wired into this system, so I got a Nest installer from their site.

 

[buzzlightyear]

Yes, builder provided plumber and electrician. Neither knew how to get multiple Nest thermostats wired into this system, so I got a Nest installer from their site.

When the heating engineer came to install the 3 nests (to control separate zones on the ufh and the water) we ran into issues.

IS IS THE NEST INSTALLER ?

 

[LFletcher]

Wonder why the boiler is on a 16A RCBO?

I can't tell you why it's on a 16A RCBO, but I do know it's on it's own 2.5mm radial circuit, as is the Megaflo and there's also a MVHR on it's own radial.

The house was built in the 40's and the whole thing was on 3 rings - which were flakey at best.

As there are only 3 original walls left I took the opportunity to get them to rip out everything and start again. I have a 28 way consumer unit with everything much more granular - each room practically has its own ring now. It's massive overkill, but I have quite a bit of computer equipment which I didn't want other things in the house taking out if something tripped.

 

[LFletcher]

IS THE NEST INSTALLER ?

Not sure I follow - is the nest installer what?

 

[telectrix]

take no notice of Buzz. he's from another planet, deep inside the Romulan Empire.

 

[Leesparkykent]

All you need is a nest thermostat and a heat link for each zone. The Heat link will control the valve for each zone which in turns switches the boiler. Or in your case the heatlink controls the actuator or thermostat terminals on the UFH wiring centre which in turn switches the valve which switches the boiler.

 

[buzzlightyear]

so I got a Nest installer from their site.

When the heating engineer came to install the 3 nests (to control separate zones on the ufh and the water) we ran into issues.

now are getting some where.

 

[PEG]

Am i the only person wondering what on earth,made things more "granular"?

 

[LFletcher]

All you need is a nest thermostat and a heat link for each zone. The Heat link will control the valve for each zone which in turns switches the boiler. Or in your case the heatlink controls the actuator or thermostat terminals on the UFH wiring centre which in turn switches the valve which switches the boiler.

The Nest heating engineer wired up the nests to control the ufh heating zones and that all appears to work as expected (nest 1 opens 4 actuators, nest 2 opens the next 2 etc). His issue arose when trying to switch on the boiler from the ufh wiring centre. I shall double check with him today that he's all good for the weekend and that he's confident everything will be wired correctly (and work as expected).

 

[AJshep]

Sure the "Nest Engineer" knows how RCBOs work and will fix it in no time, so I wouldn't panic too much.

We used to do alot of of heating wiring for school boiler rooms, quite often we would have a 16amp circuit with a isolator Clearly Labeled" near the Boiler to completely isolate the supply and control gear. We then put in inividual fused Spurs for pump and boilers which we could fuse down accordingly, reason we would do it like this is because some of the pumps were pretty big.
I enjoyed it though as got to do a fair bit of metal conduit and play with some relays. Most things are done with PLCs now though.

 

[davesparks]

As far as I can tell there are 2 x 3 core and earth (1mm) running from the wiring centre in the loft to the wiring centre by the ufh heating manifold. I assumed (incorrectly?) that this was to be used for control rather than control and power to the manifold/pump downstairs?

The one saving grace is that if it is wrong it's still possible to get a cable from the loft to the utility room if required.

Usually only one 3c&e cable is required between ufh manifold and boiler for both power and control.

 

[davesparks]

The Nest heating engineer wired up the nests to control the ufh heating zones and that all appears to work as expected (nest 1 opens 4 actuators, nest 2 opens the next 2 etc). His issue arose when trying to switch on the boiler from the ufh wiring centre. I shall double check with him today that he's all good for the weekend and that he's confident everything will be wired correctly (and work as expected).

Nest engineer? I thought you said earlier that you used a nest pro installer?
Nest pro installers are anyone and everyone who wants to sign up for it, no qualifications or knowledge are necessary. I would say that based on what has happened the one you have employed hasn’t got a clue about electrical installation work or electrical safety.