Discuss Wet UFH pumps causing RCD tripping in the Central Heating Systems area at ElectriciansForums.net

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I have a customer with a problem of RCD tripping caused by the wet UFH systems.
There are 5 UFH areas each with a Wilo Para pump attached. Along with this there are 5 Grundfos pumps assisting the flow of water around the property.
The System is setup with Heatmiser NeoStats wired through the Heatmiser UH8 & UH4 wiring centres.

The Ground floor UFH system has a boiler demand cable that signals a 2 port valve and a Grundfos pump to operate. The 2 port then signals the boiler to fire.
The 1st & 2nd floor UFH systems boiler demands are connected and signal a 2 port valve and Grundfos pump.
There are 2 smaller systems in the Annex that are connected, operating another 2 port and Grundfos pump.

Along with this there is a towel rail circuit with a 2 port and a Grundfos pump controlled by a Heatmiser Neostat Timer and a hot water circuit also with a 2 port and Grundfos pump.

The system has been working for about 3 months without any problems until the customer finally moved in. Approximately 2 weeks after moving in the RCD controlling the central heating has started to trip. If I turn off the 1st & 2nd floor UFH everything operates fine. If I turn off the ground floor and then turn on the 1st & 2nd floor everything works fine.

The first thing I checked was picture hanging over the stat positions, no cabling has been damaged.

The RCD in the CU is a 100A 30mA and has the boiler, 2 x UFH, Hob, Microwave, Oven, Immersion with secondary pump, Annex lounge sockets.
I have checked the insulation resistance of all the other circuits and they are all over 300M ohms so nothing that can affect the RCD.

Turning on the UFH, the wiring centres go through a start up process then send power to the Neostats. They in turn go through a start up process and then turn on sending a signal back to the wiring centre to turn the boiler on. It's at this point that the RCD trips.

I have unplugged the pumps on the UFH manifolds and the system doesn't trip when the Neostats send the signal back.

I am thinking that the pumps are faulty, but when checked independently I can find no actual fault.
My question is why when one system is switched off the system operates OK and then when the power to the systems are switched around the system works OK but with all the systems on it trips the RCD?

RCD ramp test indicates that it's tripping around 19mA.
1/2 test indicates no problems.

Any help appreciated.
 
A very VERY quick guess is that it's possibly cumulative leakage from all the electronics and additional devices now been introduced by habiting the property.

Is there a compelling reason as to why the heating system needs to be RCD protected? I'd normally try and avoid an RCD in that situation, especially with that many pumps. If it's down to the supply cable being buried in walls, then maybe look at placing it on an RCBO.
 
That is one complicated UFH system! I've never got above three pumps with any I've installed.
The system is sharing a RCD with a couple of known common culprits for N -E leakage, so are you sure that the tripping isn't being caused by this when inductive loads on the UFH kick in?
I'd consider moving the UFH feed to another RCD as a test, or to fit it with its own RCBO and see if this stops the tripping, or transfers it.
 
Check the basics

could there be a N to E fault in the heating system or elsewhere?
is the entire heating system including remote valves fed from the same rcd?
N in correct N bar.
 
A very VERY quick guess is that it's possibly cumulative leakage from all the electronics and additional devices now been introduced by habiting the property.

Is there a compelling reason as to why the heating system needs to be RCD protected? I'd normally try and avoid an RCD in that situation, especially with that many pumps. If it's down to the supply cable being buried in walls, then maybe look at placing it on an RCBO.
I was thinking about possible cumulative earth leakage, and I haven't tried disconnecting the other items to see if it works without them connected.
RCD used as all wiring <50mm in walls and there are 25 wired Neostats within the property.
 
That is one complicated UFH system! I've never got above three pumps with any I've installed.
The system is sharing a RCD with a couple of known common culprits for N -E leakage, so are you sure that the tripping isn't being caused by this when inductive loads on the UFH kick in?
I'd consider moving the UFH feed to another RCD as a test, or to fit it with its own RCBO and see if this stops the tripping, or transfers it.
The RCD generally trips over night so other appliances are on but not being used.
Forgot to mention this is a new build and all appliances are new.
I will try to move to an RCBO to test.
 
Check the basics

could there be a N to E fault in the heating system or elsewhere?
is the entire heating system including remote valves fed from the same rcd?
N in correct N bar.
All neutrals are on the correct side of the board.
All heating system is fed from the same RCD
 
The RCD generally trips over night so other appliances are on but not being used.
Forgot to mention this is a new build and all appliances are new.
I will try to move to an RCBO to test.
Not being used is irrelevant if the isolator is on.
 
I was thinking about possible cumulative earth leakage, and I haven't tried disconnecting the other items to see if it works without them connected.
RCD used as all wiring <50mm in walls and there are 25 wired Neostats within the property.
If the RCD is going at 19mA you've got very little overhead at all for 'normal' leakage. If you've a decent mA leakage clamp meter then now's the time to use it. If it were me I think I'd be looking to find ways of breaking that down into at least a couple of separate circuits and spreading the discrimination. You can always use a contactor to bring them back together again.
 
If the RCD is going at 19mA you've got very little overhead at all for 'normal' leakage. If you've a decent mA leakage clamp meter then now's the time to use it. If it were me I think I'd be looking to find ways of breaking that down into at least a couple of separate circuits and spreading the discrimination. You can always use a contactor to bring them back together again.
No leakage clamp meter as yet, any recommendations?
There is no N link between the boiler and the UFH as the wiring centres use a 0v built in relay to send the demand signal.
The remote Grundfos pumps and 2 port valves are controlled by the boiler spur, so I could separate the UFH and the boiler to 2 RCBOs
 
Not being used is irrelevant if the isolator is on.
True.
Whilst the house was being second fixed, the ovens were not in and the UFH worked fine.
It did work happily for about 4 weeks with the ovens and hob connected though.
I'll isolate the ovens and hob then test.
 
If you've tested all cabling for insulation resistance, and there is no fault, then surely that's as far as your responsibility goes?
I would be careful about splitting up the circuit, as most domestic heating systems are supposed to be capable of being isolated from a single device.
 
If you've tested all cabling for insulation resistance, and there is no fault, then surely that's as far as your responsibility goes?
I would be careful about splitting up the circuit, as most domestic heating systems are supposed to be capable of being isolated from a single device.
You'd think that was the end of my responsibility but the plumber is pointing fingers. The bit that gets me is they spec'd and supplied the system then when it trips they say it's an electrical fault. They even sent a plumber in to check it, who told the customer the 100A MCB ( not an MCB an RCD) was too small, was overloading and needed to be upgraded!!!!!!!
 
You'd think that was the end of my responsibility but the plumber is pointing fingers. The bit that gets me is they spec'd and supplied the system then when it trips they say it's an electrical fault. They even sent a plumber in to check it, who told the customer the 100A MCB ( not an MCB an RCD) was too small, was overloading and needed to be upgraded!!!!!!!
Since when did we start listening to wet pants?
 
Since when did we start listening to wet pants?
We don't listen to them, but customers will listen to the last person in the building unfortunately.
It took a while but I finally convinced the customer and the plumber that the 100A RCD didn't need to be upgraded.
 
Turning on the UFH, the wiring centres go through a start up process then send power to the Neostats. They in turn go through a start up process and then turn on sending a signal back to the wiring centre to turn the boiler on. It's at this point that the RCD trips.

The RCD generally trips over night so other appliances are on but not being used.
Forgot to mention this is a new build and all appliances are new.
I will try to move to an RCBO to test.
One post seems to contradict the other here, you can't start the system but then it trips overnight

RCD ramp test indicates that it's tripping around 19mA.
1/2 test indicates no problems.
If a brand new RCD is tripping at that level I would be speaking to the manufacturer about a replacement, out of the box problems with RCD's seem to be getting more common in the last few years
 
Possibly it is. Imo most decent rcd I’ve ramp tested with all loads disconnected are about 24-27ma. 19 is low imo. Perhaps because of cumulative earth leakage, perhaps by design, perhaps faulty.

OP says it’s Hager. Usually these are around 25ma in my experience and reliable and good quality
 

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