CH fault - 3amp fuse blowing... Help ? (New problem)

[alx]

I have a problem with my central heating system.

The system comprises of the following;
Ideal Classic FF350 boiler
Salus EP200 programmer
Salus RT300 room stat
Danfoss HSA3 diverter
Danfoss AT type tank stat
CP63 circulating pump

The system is currently set for timed HW with the CH switched off. In this mode the system works fine.
Last night I went to turn the CH on for a 1hr “boost” and the 3amp fuse in the switched spur immediately blew.
I have removed the programmer and tested the outputs, which are showing 230v on T1 and T2 when the system is off and T3 and T4 when HW and CH are called for. This to my knowledge appears in order and there appear to be no welded relays.
I have wired the pump directly to a 3pin plug with a 3amp fuse and it ran fine. I am assuming this is also in order.
I removed the HSA3 actuator. The valve itself was a bit stiff, but has loosened with some manual turning. There is no continuity between any of the feeds for the actuator. I have wired in to the 3amp fused 3pin plug via a terminal block as advised in a previous post and the fuse blew after about 5 seconds. This actuator is about 2yrs old. It’s predecessor expired in a similar manner but knocked out both HW and CH.
This pointed towards a fault with the actuator, however calling for CH with the actuators wiring disconnected still causes the spurs 3amp fuse to blow.
I have disconnected the tank stat to eliminate that and the fault remains.
I have tested the room stat with a continuity tester and it appears in order.
I am now left thinking that the only thing left with a fault could be a short in the wiring between the terminal box in the airing cupboard and the programmer downstairs – I am testing this at present.

Is there anything else I can check / test to identify my fault ?

Thanks, Alex.

 

[Agile]

Have you closely inspected the inside of the motor valve?

Any sign of leaking inside?

Tony

 

[alx]

I wouldn't be surprised if there has been a very small amount of water enter the inside of the motor valve. The screws at the bottom both have a small amount of white surface corrosion. As does the bottom of the manual arm..

The only thing that I'm finding confusing, if the actuator / valve are at fault - why is the fuse still blowing with the part removed ?

 

[alx]

Small update..

From testing continuity in the terminal box mounted in the airing cupboard, it would appear that the feed for CH-ON is shorting to earth somewhere..

 

[Agile]

"removed" ?

Do you mean you have disconnected all the wires from the head and the fuse still blows?

Tony

 

[alx]

"removed" ?

Do you mean you have disconnected all the wires from the head and the fuse still blows?

Tony

Hi Tony,

I meant that I have disconnected and removed the actuator / motor head.. The valve is still in place.. And yeah, the fuse still blows when calling for CH

 

[alx]

Another update..

The CH-On is shorting to Earth (even when removed from the programmer terminal connector and the terminal block in the airing cupboard).

I have run a test cable from the programmer to the terminal block in the airing cupboard and the fuse does not blow.

So it's looking like the cable is damaged somewhere (all of which is buried in the wall).

Any ideas how to find an earth fault ?

 

[alx]

The short is between CH-ON and the earth feed for the boiler..

Any ideas what would cause this fault ?

 

[alx]

Found the short..

The builders / kitchen fitters had put a screw through the cable beside the boiler.. Just got to replace that section of cable, reconnect the valve / tank stat and hopefully all should be well.

 

[ChrisR]

It's disconnect and test, all the way along the line.

Disconnect the switched live from the boiler (input) and try again, etc.
NB the pump might be supplied directly from the boiler , so test with that connected and n/c.
If the SL to the boiler is short to earth, then disconnect anything else comiing from the boiler...
If it's still doing it then it's time for a boiler bloke.

NB - water is very often involved in fuse-blowing!

Room stats can suddenly get a short, via wet wallpaper, a screw in the wall, etc.

 

[alx]

Fixed the short in the wall, boiler fired up but tripped after a few seconds.

Disconnected the motor head from the HSA3 and it works fine, so that has obviously blown once again.

That will be an easy job once the replacement part arrives!

 

[alx]

Well, I thought this was fixed.. But I still have problems. In-fact now it is actually worse than when I started, so today has been a complete washout!

The system ran fine heating water and the radiators for a good hour or so, at which point it tripped off, again blowing the 3amp fuse in the spur.

There appears to be no earth shorts now - except neutral to earth when the switched spur is turned on (that is normal with the main supply switched AFAIK)??

My problems now are basically as follows;

Turn the spur on, call for water and the fuse blows instantly.

Turn the spur on and call for CH and nothing happens.

I have tested the programmer outputs with a voltstick and to be honest, it appears to be showing erratic outputs to the CH/HW ON /OFF feeds.. I suspect it is probably the cause, but would like to check if the system fires without replacing it (don't want to add another thing to the shopping list if it is not the cause).

The pump was disconnected and wired directly to the mains using a 3pin plug and 3amp fuse. I ran it for 1hr and it didn't pop the fuse, and still sounds to be working ok.. I am making the assumption that this is not the cause of the fault.

The tank stat was removed and seems to be switching ok.. Is there any other way to test it ?

The HSA3 is still not connected. It is sat on my desk as I'm fairly confident that part has blown.

Any help; instructions how to test various components or the wiring itself would be most appreciated. I've packed up for tonight, but will be back on it first thing in the morning.

Cheers for any help!

 

[Agile]

Disconnected the motor head from the HSA3 and it works fine, so that has obviously blown once again.

You keep on saying thjat you have disconnected the valve head!

Again, I ask you does that mean disconnectiong all the wires?

Or do you just mean you have removed it from the valve body but LEFT all wires connected ( and the same fault condition potentially inside! )

Tony

 

[alx]

Sorry..

By disconnected, I mean it's sat on my desk. Removed from the valve and all four wires removed from the terminal block.

 

[alx]

System is now working with HW. I had made an error with the wiring of the tank stat which I overlooked yesterday..

I do still have an issue, but I'll start another thread for that.

Thanks