heating only blowing fuse

[youngplumb13]

Hi

I have been trying to resolve a problem with the 3 amp fuse blowing when i switch the programmer to heating only.The system is a y plan and at first I thought there was a wiring problem so I sourced all the cables identified them and made sure it was wired correctly.

As i knew the problem was with heating only I disconnected the heating on wire form the programmer to start a process of elimination .Even with the heating on wire disconnected which initailly goes to the room stat the programmer blows the 3mapfuse when switched to heating.I put a new fuse in and with programmer front temporarily off checked voltage and polarity both o.k.I was lucky enough to have different programmer in my stock to try and the same fault occurs.

The RCD never trips at fuse board so I dont think its an earth problem.The plot has thickened in that the fused spur is now not allowing power through it.

any suggestions and help appreciated

Thank you!

young plumb

 

[sherbert]

think about what is happening thats different from the hot water being on

If its a y-plan the motor on the 3-port valve has to move??

Try a new sychronous motor would be my first thoughts

 

[RF Lighting]

Does the system still work when both CH and HW are called for, and also just HW?

 

[petertheplumber12]

You need to do a more comprehensive test with the multi meter, Something is drawing too much current when on. more isolation of wires and testing is needed to see where the prob is. The rcd trips when something live or neutral shorts to earth, the mcb trips when current drawn is exceeding mcb rating the 3 amp fuse is less than mcb that's why it blows. It cant be pump because it's ok on hot water, it can't be boiler for same reason, it could motorised valve or wiring in junction box.

 

[MeldrewsMate]

If it's a standard backplate on the programmer (N, L, 1, 2, 3, 4) then term 4 is connected to L by the programmer when the heating is on, and term 2 to L when the heating is OFF.

Do you have a connection to term 2? You should only have wiring on terms 1, 3, and 4.
Check the cylinder thermostat is correctly wired, if in doubt start by disconnecting all 3 wires at the terminal box (not at the cyl-stat or you'll have loose live wires).

An RCD will not trip on a line to neutral fault, but the fuse WILL blow (there's a clue there).

Finally, if the spur (Fused connection unit?) won't allow power through, you've got to fix that fault before you've any hope of the system working. Check the L(out) and N(out) wiring is correct and secure, and use a multimeter (or proper GS38 tester) to test for 240vac out.

And if you can't work safely, don't.

MM

 

[petertheplumber12]

I was writing mine while you 2 were entering yours. Ha Ha.

 

[joe-90]

You haven't said if the system ever worked correctly. If it did then something has changed and you need to find out what it is. If it has never worked then you can guarantee you've wired it wrong. Which is it?

 

[youngplumb13]

ok thanks all for the help so far.

To give more info the system works fine on hot water only fires up pump and boiler and runs fine.

In my process of elimination I disconected all the wires to the room stat ,common, call, satisfied, and eath and temporarily put them in a chocolate block .Put heating on, still blew a fuse, instantly when heating pressed.

It is a standard heating system and the programmer has a standard backplate.There was a connection on 2 heating off previously as someone had wired in a frost stat incorrectly so its live was supplied when there was no heating demand and then if the frost stat was calling , closed circuit the live fed back to terminal 4 heating on at the programmer. I removed this as I knew it was wrong and should be permanent live in to frost stat and demand out to junction box to meet white wire on 3 port valve.

The old system did work when I arrived on hot water .On heating however the room stat was broken and when the dial was turned did not make a heating demand.I had to replace the room stat as I knew it was broken with all wires diconnected the mechanical stat did not make a demand when turned up i checked by checking continuity acorss common and demand closedf circuit.I am satisfied the new stat is wired correctly and as explained the fault does still occurs with the stat wire disconnected safely anyway.

Thank you all for your help , genuinely appreciate the guidance from people with a greater expereince than me

perhaps ill be able to retuen the favour in the future to soemone else.

 

[matt1e]

Hi

I have been trying to resolve a problem with the 3 amp fuse blowing when i switch the programmer to heating only.The system is a y plan and at first I thought there was a wiring problem so I sourced all the cables identified them and made sure it was wired correctly.
)

does the heating work ok when the hot water is also on?

 

[youngplumb13]

i havnt checked that yet will try it next.

thanks

 

[cowley]

If it's a Honeywell Y plan could be micro switches in motorised valve check for water getting into micro switches.

 

[cowley]

If it's a Honeywell Y plan could be micro switches in motorised valve check for water getting into micro switches.

 

[cowley]

If it's a Honeywell Y plan could be micro switches in motorised valve check for water getting into micro switches.

 

[cowley]

Don't know what happened there maybe water in my ipad

 

[stem]

I had to replace the room stat .....I am satisfied the new stat is wired correctly and as explained the fault does still occurs with the stat wire disconnected safely anyway.

Not sure what you mean by "the stat wire disconnected" I read this to mean you have disconnected only one wire, so if you have disconnected the switched live to the white wire on the motorised valve, What have you done with the other wires? Was there a neutral to the original stat? If so it's not connected to the live supply somehow now is it? Either by electrical connection or being trapped when the stat was replaced.

You say that the old stat didn't make electrical contact, but you didn't say that it blew the fuse. Now you've changed the stat and the fuse blows even with "the stat wire disconnected" which should be the same condition as having a thermostat that doesn't make electrical contact. Hmmm....