3 amp fuse blown twice, is it the pump?

[jackecole]

We have an older style, common central heating and hot water system. The 3 amp fuse has blown today in the spur supplying it. I have read that this is often caused by the pump or fan. Our boiler has no fan so I presume it is the pump. I have checked all leads/cables in the airing cupbaord are not pinched/uninsualted and there are no water leaks evdient.



A new fuse was put in and this also blew.

Before I replace the pump I'd like to make sure it is definetelty the cause please?

 

[Agile]

Disconnect live from the pump and replace fuse.

If it still trips its something else!

Tony

 

[seco services]

take the centre screw out of the pump see if you can rotate it.
just hold a rag under it when you remove the screw.
try disconnecting the pump and try system.
is it a fully pumped system ?

 

[jackecole]

Yep it is a Y Plan, has a 3 port mid position valve.

I have tried removing the centre screw and turned the rotor, it was sluggish. Possibly a big of sludge got in. The pump has been used though, it 's not been out of action for a long period.

Should I try another 3 amp now that the pump rotor is turning better?

 

[seco services]

Should I try another 3 amp now that the pump rotor is turning better?

i would disconnect and try it if the boiler fires up then you can try it with pump connected if it blows again you know the windings have failed etc in pump.

 

[jackecole]

Sorry I do have a fan in my boiler. I have just moved 2 weeks ago here and was thinking about our old Potterton!! The system is old style still (a Y Plan like our previous house was), but the boiler is a Potterton Suprima.

Could the fan be the cause? I'll try the pump first as suggested.

 

[Ronald0]

A blown fuse is caused by too much current being drawn by a fault in the cable or a device or a connection.

Check one device at a time. If you supect a pump fault and are competent working with mains electricity, disconnect the live supply to the pump (as has been suggested) at the wiring centre, fit good fuse and switch on heating system.

The boiler will run for a short time without a pump.

 

[jackecole]

Hi all, thank you for your great help.

I have tried disconnecting the liv ewire from the pump terminal (it is grundos by the way) and replace the fuse and turned on ch so the boiler would fire up.

The fuse was blown again.

I am confident and sensible enough to work on electrics and have a multimeter which I have used before.

What else could be the fault? The boiler fan?

 

[Agile]

Next step could be to disconnect the boiler.

However, in your case the pump should be wired to the boiler.

It can also be a motor valve. Some you can look inside the see any water leaking or burning of any components.

Tony

 

[jackecole]

Yes I believe the boiler I believe is connected to the pump through a pump overrun.

The 3 port is a Honeywell, shall I remove the head and check, the power is off already.

Could it be the fan in the boiler sticking?

Is a short circuit check possible with my multi meter?

 

[lifesagasman]

be methodical and check one thing at a time...

 

[jackecole]

I have chekced the 3 port valve and no signs of burning/water leaks here. It is fiddly to replace this head, maybe just me! Is all good again now though.

What shall I check next?

 

[Ronald0]

Short circuits are normally located by visual inspection; localised damage due to burning or melting.

Reconnect pump and disconnect MV white and orange wires from wiring centre. Switch on HW, boiler will be driven from cylinder stat demand only.

 

[Agile]

Many heating faults which blow mains fuses are caused by arcing rather than a low resistance and cannot be measured at a low voltage.

I cannot advise you to access the fan as its inside the combustion chamber. But on the old PCB you can remove its plug from the PCB.

Which PCB do you have? The old open one or the new one in a plastic box?

Rarely the PCB could have a fault. the old one had a fuse on the PCB but any fault would usually blow that.

Tony

 

[jackecole]

I have tried removing the wires from the 3 port and still no joy, fuse still blows.

Agile: arcing means a wire (uninsulated part) touching another wire (uninsulated part) /metal parts and causing a short?...

I have heard there is a test you can do where you remove the boiler's wires from the spur/wiring centre (with powe off) and test across L and N ends for resistance which should be more than 100 Ohms? This of course will then probably be under 100 Ohms and not tell me what the fault it though.

Could I remove the wires from the fan and do the test again to prove the fan is causing the short/fuse to blow?