On 16 Sep 2003 21:35:53 -0700,
(Charlie) wrote:

Hello,

I have a Honeywell wiring box into which all the components of my CH
system are wired. In the last couple of days the 2A fuse in this box
has blown (twice) and a 3A one also blew - obviously I have a problem.

The pilot light is still on. There are no signs of leaks. Presumably
it could be any of the components but presumably likely to be the pump
or the motorised value.

Depending on what the boiler is, it could be a fault there as well -
you don't say what the boiler is. Often the pilot light does not
depend on an electrical supply to the boiler working.


I have tightened all the wiring connections in case there was any
loose connections - there weren't.

Th other thing to look for is whether there are any places (and it
could be anywhere on the system) where the insulation on a wire might
have been nicked or possibly chafed by it going through a hole in
metal without a rubber or plastic grommet. Boilers can be
favourites for this if the installer was lazy.

My problem is how do I check these components if I have no power to
test them?

The problem as well is that these are intermittent.

Could I put a 3 pin plug on them and plug them into the mains?

You could for the pump, quite easily, and the motorised valve less
easily. These have up to five wires connecting to the motor and an
auxiliiary switch inside. You need to pick the motor wires. Either
you can take the cover off of the valve head and trace the colours to
the motor or look at the manufacturer's data sheet. One thing to
watch with this is that you will be feeding the item under test from a
different power source and this means that it is not isolated at the
same time as the rest of the system if you switch that off.

I don't think that you would be able to diagnose much more than the
pump and possibly the motorised valve this way. The boiler will
typically have multiple connections and you really need to know what
you are doing and have the manufacturer's service information .

One candidate for the fault you are describing is failed insulation
and shorted turns on the motor of the pump or the valve. This can
manifest itself as intermittent - I had a pump that failed that way
once. FOr any of these tests, don't use more than a 3A fuse.


What could I put temporarily and safely across the fuse holder to keep
the system running for a while while I test it.

NOTHING other than the correctlhy rated fuse. The 2A and 3A fuses
are there to protect the system and you. The 6 inch nail approach
can result in more damage or even a fire so don't be tempted.



Email replies to my address without the hotmail extension and
replacing the underscores with common email characters.

If I got a circuit tester what checks could I carry out with or
without the power on?

On an intermittent fault, I don't think that you will see all that
much.


I do recall a plumber coming to my last house, putting a circuit
tester across the pump terminals and instantly telling me I needed a
new pump. But he of course had power.

It could have been a failure that was an open circuit, a short circuit
or even an insulation breakdown to earth.



Finally what would I expect an CH electrical engineer to charge me to
do the relevent checks (North London)?

You might want to look back through recent posts and find Ed Sirett.
His email address is in his signature and is in North London.


All help gratefully received.

Charlie

..andy

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