Electrical test procedure on a gas boiler

M

martineire

Quick question regards electrical test procedure on a gas boiler. I've isolated the power via removing fuse from spur but the problem is when doing my earth continuity, short circuit test and resistance to earth checks I'm getting different resistance reading when the spur switch is turned on and off. Fuse is removed and all clocks and stats are calling for heat but with the spur switch on I'm getting difference reading than when it's switched off?? Earth continuity is grand it's less that 1 OHM but with the other two tests I'm getting confused and need advice

Fuse out with switch on

Live and neutral= 187 OHMS
Live and earth =186 OHMS
Earth and neutral = 000.7 OHMS

Fuse out with switch off

Live and neutral= 183 OHMS
Live and earth= OL
Earth and neutral= OL

My live test I'm getting

Live and neutral= 231V
Live and earth= 231V
Earth and neutral= 17V

Any advice and help thanks
 
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I have no idea if 180ish ohms is as it should be but the results are what you would expect.

What are you trying to prove or discover?


You could try asking in the Plumbing and Central Heating section where you will be told you are not allowed to do it.
 
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Fuse out with switch on

Live and neutral= 187 OHMS
Live and earth =186 OHMS
Earth and neutral = 000.7 OHMS
Fuse removal only breaks the line(live) conductor.
So, neutral and earth are still connected at source.
As above, I don't know what the resistance through the boiler would be.

Fuse out with switch off

Live and neutral= 183 OHMS
Live and earth= OL
Earth and neutral= OL
Switch being double pole has also broken the neutral.

My live test I'm getting

Live and neutral= 231V
Live and earth= 231V
Lowish but acceptable.
Earth and neutral= 17V
Would probably disappear with a low resistance meter.


These tests (apart from probably pointless 180Ω) have nothing to do with the actual boiler but merely the circuit to it.
 
M

martineire

EFLImpudence";p="3112354 said:
These tests (apart from probably pointless 180Ω) have nothing to do with the actual boiler but merely the circuit to it.
theses tests are preformed at the boiler terminal strip with the appliance isolated. They should be testing the boiler and not the circuit
 
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Earth and neutral= 17V
Would probably disappear with a low resistance meter.
UMM

If the voltage between earth and neutral disappears with a low resistance meter than you have a problem because that would mean at least one of your neutral or earth is not properly connected.
 
M

martineire

Fuse out with switch on

Live and neutral= 187 OHMS
Live and earth =186 OHMS
Earth and neutral = 000.7 OHMS
Fuse removal only breaks the line(live) conductor.
So, neutral and earth are still connected at source.
As above, I don't know what the resistance through the boiler would be.

Fuse out with switch off

Live and neutral= 183 OHMS
Live and earth= OL
Earth and neutral= OL
Switch being double pole has also broken the neutral.

My live test I'm getting

Live and neutral= 231V
Live and earth= 231V
Lowish but acceptable.
Earth and neutral= 17V
Would probably disappear with a low resistance meter.


These tests (apart from probably pointless 180Ω) have nothing to do with the actual boiler but merely the circuit to it.
So am I right in saying to preform theses tests on the boiler and the boiler only (Not the source) I have the isolate at the fuse spur by removing the fuse and also turning the switch off to break the neutral seen it as a double pole spur.
 
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If you are testing the BOILER then isolate the supply, remove the connections at the BOILER and test the BOILER.
Remember that the wiring from the fused spur may well go to all sorts of other heating items such as pumps and valves too, so make sure that you have isolated only the bit you are testing or you will get strange results.

But you have not answered the key question
there are a number of things that can be electrically tested on a boiler, what is the purpose of this testing?
 
M

martineire

Just to remind you of these questions also, if you are not willing to expand, how can we help?
What exactly are you testing?
Why?
What with?
Theses test that I'm performing are standard tests that have to be preformed on a gas boiler before you service that boiler. The four tests to be completed are earth continuity, short circuit, resistance to earth and polarity. Three tests are done with the boiler isolated and obviously polarity is a live test. Theses tests are testing the boilers internal components and wiring looms within the boiler itself and not the source. Tests are being completed with a auto range multimeter.
 
M

martineire

Really I just want to understand why am I getting a resistance reading between L and E when fuse is removed from spur but switch is on and why I'm not getting a resistance reading for L and E when fuse is removed from spur and switch is off. Earth shouldn't be meeting Live either way.
 
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Really I just want to understand why am I getting a resistance reading between L and E when fuse is removed from spur but switch is on and why I'm not getting a resistance reading for L and E when fuse is removed from spur and switch is off. Earth shouldn't be meeting Live either way.

Because you're reading through the neutral/earth connection.
 
M

martineire

Really I just want to understand why am I getting a resistance reading between L and E when fuse is removed from spur but switch is on and why I'm not getting a resistance reading for L and E when fuse is removed from spur and switch is off. Earth shouldn't be meeting Live either way.

Because you're reading through the neutral/earth connection.
well then would I be right in saying that by switching the switch off as well as removing the fuse from the spur I am breaking that connection and as a result just testing the L and E (resistance to earth) through the boiler? And that's the right way to properly isolate
 

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