If the heating system is wired correctely it is not possible for the pump to remain running when the spur fuse blows. are you sure that the fuse you refer to is the one for the electrical supply to the heating system?.
Central heating system blowing fuses
- Thread starter ottosump
- Start date
If the heating system is wired correctely it is not possible for the pump to remain running when the spur fuse blows. are you sure that the fuse you refer to is the one for the electrical supply to the heating system?.
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The op was asked to power the pump seperately to eliminate it as the cause of the fuse blowing.
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Update for the above, fitted new randall 103 timer this afternoon, ordered one of EBay, then found out that my cousin had brand new one in his cupboard, typical. Anyways, made no difference, still blowing fuse, checked wiring again and removed cylinder thermostat from the equation & the diverter valve. Heating would not fire up, but did not fuse either, could hear randall timer running, re-connected cylinder thermostat and the fuse blew straight away. Upon inspection I noticed the following. Cylinder stat fitted to terminal block as follows, Brown-T2, Earth-T6 & Blue T7. When I connect the brown to T2 and checked it only shows voltage when system is turned on, when it is showing 240ac the Earth on T6 is also showing 240v AC, this I would predict is the cause fault I have been getting. Its an old Sunvic Type SA1452 clamp on thermostat, I believe these are now discontinued.
whilst removed the boiler won't fire, is this because I have the diverter valve disconnected. I can refit the diverter wiring but would appreciate the following advice as I'm unsure which terminal the blue wire connects to from the valve, I believe it was set up as the Blue (possibly T4 or T5) T4 has x1 yellow wire connected & T5 has x3 blue wire connected ( excluding the blue I need to connect)
Also, Is there an alternative for the above thermostat (Sunvic Type SA1452)
Regards Otto
whilst removed the boiler won't fire, is this because I have the diverter valve disconnected. I can refit the diverter wiring but would appreciate the following advice as I'm unsure which terminal the blue wire connects to from the valve, I believe it was set up as the Blue (possibly T4 or T5) T4 has x1 yellow wire connected & T5 has x3 blue wire connected ( excluding the blue I need to connect)
Also, Is there an alternative for the above thermostat (Sunvic Type SA1452)
Regards Otto
I seem to remember we had someone with an intermittent fuse blowing.
It turned out to be the cyl stat was wrongly wired but only a certain combination of situations caused the short.
The wiring may need to be checked wire by wire!
Tony
It turned out to be the cyl stat was wrongly wired but only a certain combination of situations caused the short.
The wiring may need to be checked wire by wire!
Tony
not contradictory at all
lets assume he has a S or W plan fully pumped gravity fed system
(with a incorrectly wired/knakered cyl stat or diverter/3-port valve)
as spraggo has said blue is normally neutral
make of valve and some photos of wiring/valves etc would be useful
Matt
I'll nip around and get some photo's today, I have the stat with me, the wiring is standard 3 core rubber flex, The earth connects to T1 on the stat, blue to T2 & Brown to T3, there is also an earth terminal with no wiring connected to it, the wiring has not been altered on the stat and has been faithful for approx 20 years.
I guess my earlier query with regards to why the earth was indicating 240ac on the cylinder stat is probably due to the fact, the earth wire has been utilised for when the stat is closed, so it is probably not at fault.
Regards Otto
Pictures up soon
I guess my earlier query with regards to why the earth was indicating 240ac on the cylinder stat is probably due to the fact, the earth wire has been utilised for when the stat is closed, so it is probably not at fault.
Regards Otto
Pictures up soon
Finally, this has been a long one. The Earth returning from the cylinder stat as mentioned was live. I assumed that it was the earth, it was not, it was the demand as mentioned. I had taken the wires out of the terminal block umpteen times to try and diagnose the fault, when I had replaced the wire I made the presumption that the earth returned to the terminal containing a block of x3 earths, this was the wrong assumption. When I returned the demand wire to its correct terminal the boiler fired. The fuse remained intact and has ran for a fortnight, until now, another problem has manifested which I will raise in another thread.
So the problem was the randal timer mechanism, which I swapped out and all was well.
Thank you for all your help and advice, it was invaluable, Otto
So the problem was the randal timer mechanism, which I swapped out and all was well.
Thank you for all your help and advice, it was invaluable, Otto
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