ABNORMAL EARTH LOOP TEST AT BOILER

[jwphillips]

Looking for advice re failed earth test. Combi boiler goes dead. Gas engineer advises earth loop test failure with reading greater than 200ohms. Advises Electrical inspection. Electrical engineer reconnects earth clamp at gas meter that was disconnected and fixes supplementary bonding to pipes at boiler. Advises earth continuity greater than 200 Mohms and earth loop impedance 0.60ohms. Gas engineer returns and advises earth loop test failure again within boiler. Isolates boiler at fused spur and diagnoses fault with Ignition PCB. Now awaiting replacement part, but boiler still condemned for having poor earth. Whose advice is incorrect? Could the Ignition PCB problem beihng causing the failed earth loop test? Would appreciate any advice as have children of 1 and 3 and have no central heating or hot water.
Thanks

 

[ricicle]

How many 'engineers' have carried out tests here?

The only true way to confirm earth continuity to the FCU is an R1+R2 test (or R2 test)

Was the test just a Zs test at the FCU. 0.6 ohms seems pretty good (depending on the protective device), but could be due to parallel paths.

200 Mohms is too high for earth continuity.Was this for the bonding to the gas?
Where is this boiler located?Supplementary bonding is not required if it is in a kitchen.

Was an earth continuity test carried out on the earth wire in the flex between the FCU and the boiler mains connection?

I think someone has their 'wires crossed' somewhere.

 

[JohnD]

Although it's only in a kitchen, boiler engineers like to supplementary bond all the copper pipes (gas and water) going into a boiler to its supply and its chassis. thsi is not an electrical regulation but gives them confidence they will not get a shock from touching two pipes. It's quite common and no prob. the incoming gas and water are probably metallic and main bonded a few metres away so will give parallel paths.

I don't understand "earth loop test failure again within boiler" but maybe there is a fault between the FCU and wherever he was testing.

 

[jwphillips]

How many 'engineers' have carried out tests here?

The only true way to confirm earth continuity to the FCU is an R1+R2 test (or R2 test)

Was the test just a Zs test at the FCU. 0.6 ohms seems pretty good (depending on the protective device), but could be due to parallel paths.

200 Mohms is too high for earth continuity.Was this for the bonding to the gas?
Where is this boiler located?Supplementary bonding is not required if it is in a kitchen.

Was an earth continuity test carried out on the earth wire in the flex between the FCU and the boiler mains connection?

I think someone has their 'wires crossed' somewhere.

Wires crossed indeed. Boiler located in cupboard space in bathroom. Can't answer your technical queries unfortunately. From memory earth continuity test was conducted at boiler between mains connection and earth terminal on Ignition PCB. Does that help? Has my sparks given me poor advice?

 

[JohnD]

I think ricicle may be right about "the earth wire in the flex between the FCU and the boiler mains connection" unless there is a bad connection in the boiler.

I would have hoped the electrician would have tested up to the FCU but wouldn't expect him to be trained to work under the covers of the gas boiler.

but I don't really understand what can have happened

 

[Paul Barker]

It seems to me that if the R2 at the fcu and the zs at the fcu is cock on, then it is the boiler service engineers job to find the fault.

Under the protective cover to protect the electronics from leaks there are usually a number of spade connector made earth connexions. I would be testing these in the first instance.

 

[Paul Barker]

Although it's only in a kitchen, boiler engineers like to supplementary bond all the copper pipes (gas and water) going into a boiler to its supply and its chassis. thsi is not an electrical regulation but gives them confidence they will not get a shock from touching two pipes.

It's all steaped in steaming bulls doodoo. No gas fitter wants to do all this blessed bonding, it's just that many MI's are now demanding it because they are writen by clowns who haven't enough intelligence to understand the meaning of 7671.

Sadly my local Napit inspector says to me that if it is in the MI's you have to do it. He frowned about it as it is a very worrying trend.

Anyhow I'm not worried about that, I only do what I consider necessary. Most boiler pipes have great continuity one to another and to the boiler as it is.

Of course fools who touch the spade connectors of fans without removing supply are probably heading for extinction under the laws of survival one way or another pretty soon now. You'll never design in enough protection for cack handed dumbos who manufacturers have tried to keep out of boilers by designing difficult case removel .