central heating keeps blowing fuse

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i have apollo 15/30 type wall mounted boiler and have an electric (i think ) fault in the system ..at first it blew the main fuse after boiler was on an hour after the heating switched off and the boiler ran on for 20 min...then several time it blew after 5 minutes of switching heating on..ive replaced the thermostat and acuatator ..(usual suspects )and still blows the main 5amp fuse/...the acuator box fuse (5amp) and boiler fuse (5 amp ) (switch just below the boiler ) doesnt blow...just the mains one ...could it be the main pump either internaly leaking into the pump /...i can understand the fuse going with the pump hot..but it now blows with the pump cold after 5mins on..the pump seems to be working during that 5 mins ...can the pump be the problem.. ?any answers please this driving me nuts !..all other electrics are fine
 
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Welcome to the mad house. :D

I know a bit about boilers / plumbing and electrics (but I'm not a plumber or electrician). However I just cannot get my head around your problem. It might just be terminology, for example when you say "main fuse" I think something in your consumer unit (fuse box). And is your "actuator box" a diverter valve?

You might want to try asking in the plumbing section, It's sometimes scary there but there are some heating engineers who may understand your problem.

You could also try to re-post with proper sentences and stuff to make it easier to read. And if you can attach pictures to help explain then that often helps.

Best of luck.
 
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Welcome to the mad house. :D

I know a bit about boilers / plumbing and electrics (but I'm not a plumber or electrician). However I just cannot get my head around your problem. It might just be terminology, for example when you say "main fuse" I think something in your consumer unit (fuse box). And is your "actuator box" a diverter valve?

You might want to try asking in the plumbing section, It's sometimes scary there but there are some heating engineers who may understand your problem.

You could also try to re-post with proper sentences and stuff to make it easier to read. And if you can attach pictures to help explain then that often helps.

hi thanks for reply sorry about confusing post but probbaly me banging head against the wall trying sort this ! lol ...
the acuator box is where the Thermostat and Acuator (thats the valve which sits on the divertor 3 way valve near the pump )..plugs into theres a relay 5 amp fuse and wiring connectors from the mains go into..the main fuse is the 5amp fuse in the main fuse box which is for the central heating system) thats the one that keeps fusing ...could post this on to the heating plumbing section but im not allowed to duplicate posts..anyway as this is an electric fault i thought this would be better posted here
 
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As it is a fuse which keeps 'fusing' you obviously have something which is overloading the circuit or causing a short circuit.(I would ask you if it is an RCD but as there are no 5A ones will take it as read)

As you have replaced the thermostat and actuator that only leaves the pump.

Does the pump sound like it is 'struggling'?
 
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hi thanks for reply sorry about confusing post but probbaly me banging head against the wall trying sort this ! lol ...
the acuator box is where the Thermostat and Acuator (thats the valve which sits on the divertor 3 way valve near the pump )..plugs into theres a relay 5 amp fuse and wiring connectors from the mains go into..the main fuse is the 5amp fuse in the main fuse box which is for the central heating system) thats the one that keeps fusing

No problem mac. I still not sure anyone can help you given your description of the problem.

Type slower, ask a friend to check it before you post, re-read it yourself. Some people on this forum like to help but need something to go on.
 
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As it is a fuse which keeps 'fusing' you obviously have something which is overloading the circuit or causing a short circuit.(I would ask you if it is an RCD but as there are no 5A ones will take it as read)

As you have replaced the thermostat and actuator that only leaves the pump.

Does the pump sound like it is 'struggling'?

My mains fuse box has the "wire" type fuses not the modern trip switch and the central heating circuit is 5amp ! The boiler switch fuse origionally had a 13 amp fuse so i changed it to the required 5 amp (some systems use 3 amp) ..the Control Box which house the other fuse is also 5amp ! as far as i can ascertain the fuses in the Control Box and Boiler Switch dont blow so the overload must be elsewhere !..i know pumps are prone to blowing the main fuse when they overheat but as the mains fuse blows after 5 minutes of operation could rule the pump out but could the pump short out shortly after switching on ?..perhaps the best way of checking the pump is to disconnect and isolate the main live and run the boiler on hot water only to see if the fuse goes then ..if it doesnt the pump would be the culprit ?
 
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The heating should be fused at 3A in the switched fused spur.

Your fusebox seems dead out of date and ready for upgrading for a modern RCD unit with much better safety.

To check out the pump fit a mains lead from it to plug it into a socket and see what happens. Put a 3A fuse in trhe plug top.

Tony
 
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As it is a fuse which keeps 'fusing' you obviously have something which is overloading the circuit or causing a short circuit.(I would ask you if it is an RCD but as there are no 5A ones will take it as read)

As you have replaced the thermostat and actuator that only leaves the pump.

Does the pump sound like it is 'struggling'?

You mentioned is the pump "struggling " not sure as its only on several minutes before the fuse goes !. and theres not enough time for the water to go round the radiators etc ...i wonder if its partially seized whether that would cause the overload !
 
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When I have told you what you can do to confirm the pump is the problem all you can do is to continue to "wonder".
 
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The heating should be fused at 3A in the switched fused spur.

Your fusebox seems dead out of date and ready for upgrading for a modern RCD unit with much better safety.

To check out the pump fit a mains lead from it to plug it into a socket and see what happens. Put a 3A fuse in trhe plug top.

Tony

Wonder ? ?? Well i didnt get this post till later ! ..yes thats the next step is to wire the pump lead to a plug ! The pump is old (a grundfos 15/50 model u418 class f and is over 18 years old at least) .. ill do that in next day or so !.. i agree with you about the old fuse box needing changing as everything has a certain lifespan ! Many thanks for your help ..ill keep you posted . Talking of the pump on a possible replacement does it matter about matching the exact details on the pump ie speed /pressure settings as mine is so old the modified replacement will have differant settings !
 
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hi i have a suspicion what the problem is but if i tell you you have to promise to get an rgi to fix it :p no one has got it yet.
 
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