central heating fuse blows randomly

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i have been asked to look into a boiler system that blows the 3a main fuse in the spur occasionally ie 4months apart then three fuses in a row
the system contains 4 zone valves controlling 2 hot water cylinders with individual cyl stats central heating via room stat and under floor heating with 5 manifold heads & dedicated pump and zone valve controlled via two roomstats. roomstat 1 that controls the zone valve and pump and 1 room manifold heads and roomstat 2 stat that only controls room 2 manifold heads and will not fire the boilers, UFH zone valve and pump without roomstat 1 in operation
two boilers connected in parallel and have internal pumps
i have checked the connections and they appear to be correct could this be a problem with sticking pump or valve causing overload has any 1 encouterd this type of problem before
 
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Work out the total loading of this far larger than normal heating system, it occurs to me that the electrical loading may be getting a bit close to a 3a fuse, suspect that a 5a fuse may be more appropriate, if there is a requirement for a particular piece of plant to be protected by a 3a fuse, then a secondary fuse may have to be installed to satisfy that need consult a Part P sparky for advice ;)
 
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Work out the total loading of this far larger than normal heating system, it occurs to me that the electrical loading may be getting a bit close to a 3a fuse, suspect that a 5a fuse may be more appropriate, if there is a requirement for a particular piece of plant to be protected by a 3a fuse, then a secondary fuse may have to be installed to satisfy that need consult a Part P sparky for advice ;)
re total load
zone valves 6w x 4
boilers 110w x 2
under floor heating heads 4w x 5
programmer 4w
room stats x3
cyl stat x2
total less than 720w (3a fuse)
tried a 5 and it blew that aswell then just started working again just wondering if a zone valve or manifold head was sticking a bit would it draw more power to switch over
 
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have you looked for a water leak dripping onto an electrical part, especially around a pump or motorised valve but maybe in the boiler?
 
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Work out the total loading of this far larger than normal heating system, it occurs to me that the electrical loading may be getting a bit close to a 3a fuse, suspect that a 5a fuse may be more appropriate, if there is a requirement for a particular piece of plant to be protected by a 3a fuse, then a secondary fuse may have to be installed to satisfy that need consult a Part P sparky for advice ;)
re total load
zone valves 6w x 4
boilers 110w x 2
under floor heating heads 4w x 5
programmer 4w
room stats x3
cyl stat x2
total less than 720w (3a fuse)
tried a 5 and it blew that aswell then just started working again just wondering if a zone valve or manifold head was sticking a bit would it draw more power to switch over

You seem to be quite knowledgeable. You will probably know then that motors of which there are many in your system draw maybe 3 times as much current when they are starting. The rated current is the steady current after the motor has started.

At certain times in the system two or more motors might start at the same time.

Furthermore

Occasionally boilers break down when all parts appear to test reasonably OK. That is to say if you take individual resistances of fans and pumps and gas valve coils at the windings, they appear reasonable. But the component is still faulty at start up due to shorted truns which during dead test don't show up. The way to test for this is to put an ameter ideally a clamp meter on each part and power it from a flying leed, see what current it draws. Sometimes you end up just changing the most likely part, quite often a fan sometimes a pump.

I have not yet known it to be a pcb, In my short experience it has always been a component outside of the pcb which blows fuses. There are parts on pcb's which fail, but they don't normally pull sufficient current to blow a main supply fuse as they fail. Particularly as the pcb has a .5 or 1 amp (which is not normally a slow blow fuse, though there are exceptions) fuse so discrimination is very good. However I have had a scenario where the fan on a Glowworm micron failed but didn't take out the equipment fuse inside the Micron, the shock then took out the pcb of the Boilermate 2000. But Boilermate 2000 pcb's die at the slightest hint of system trouble. A good source of revenue for the company who sell them out at £120 but probably buy them in for less than a 10er, since they are made in Eastern Europe.
 
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Work out the total loading of this far larger than normal heating system, it occurs to me that the electrical loading may be getting a bit close to a 3a fuse, suspect that a 5a fuse may be more appropriate, if there is a requirement for a particular piece of plant to be protected by a 3a fuse, then a secondary fuse may have to be installed to satisfy that need consult a Part P sparky for advice ;)
re total load
zone valves 6w x 4
boilers 110w x 2
under floor heating heads 4w x 5
programmer 4w
room stats x3
cyl stat x2
total less than 720w (3a fuse)
tried a 5 and it blew that aswell then just started working again just wondering if a zone valve or manifold head was sticking a bit would it draw more power to switch over

You seem to be quite knowledgeable. You will probably know then that motors of which there are many in your system draw maybe 3 times as much current when they are starting. The rated current is the steady current after the motor has started.

At certain times in the system two or more motors might start at the same time.

Furthermore

Occasionally boilers break down when all parts appear to test reasonably OK. That is to say if you take individual resistances of fans and pumps and gas valve coils at the windings, they appear reasonable. But the component is still faulty at start up due to shorted truns which during dead test don't show up. The way to test for this is to put an ameter ideally a clamp meter on each part and power it from a flying leed, see what current it draws. Sometimes you end up just changing the most likely part, quite often a fan sometimes a pump.

I have not yet known it to be a pcb, In my short experience it has always been a component outside of the pcb which blows fuses. There are parts on pcb's which fail, but they don't normally pull sufficient current to blow a main supply fuse as they fail. Particularly as the pcb has a .5 or 1 amp (which is not normally a slow blow fuse, though there are exceptions) fuse so discrimination is very good. However I have had a scenario where the fan on a Glowworm micron failed but didn't take out the equipment fuse inside the Micron, the shock then took out the pcb of the Boilermate 2000. But Boilermate 2000 pcb's die at the slightest hint of system trouble. A good source of revenue for the company who sell them out at £120 but probably buy them in for less than a 10er, since they are made in Eastern Europe.

cheers paul, start ups had crossed my mind forgot to take that into consideration on calcs but must have been going in the back of my mind when i was testing the system, because i let the system cool ensuring all parts ran at once. I have since found out that it has only happend twice (bleeping exagerating customers)javascript:emoticon(':rolleyes:') once a few days after the new boilers were installed around christmas and once a few days before this post, the fuse blew about two straight after each other, then is fine. suppose time will tell. but think it will do it again, then i'll just have replace one of the zone valves then alternate the removed one till each has been out of the system then replace underfloor heating pump if prob still occurs. if it happens after that then you'll be hearing from me prob in a few years :eek:
 
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