Central heating system blowing fuses

[ottosump]

Hello group, I'm currently having bother with a gravity fed central heating system. The system when switched on is blowing the 13amp fuse in the spur intermittently, it can run for a minute, an hour or a day, but at some point the fuse goes. We are getting hot water, and the radiators are getting warm, so I'd assume the pump is OK. One thing I have noticed is that the timer has a low buzz coming from it. Can anyone advise on some common faults on the system and what I should be checking for.
Regards Otto

Glow worm 35f boiler
Grundfos pump
Randal Danfoss 103 mechanical timer

 

[mr-crs]

Firstly the fuse should be 3 amp secondly is the fuse ok on hot water only and blowing on heating, this would suggest the pump is pulling to many amps and causing the problem this would be what I would check first.

 

[bengasman]

Short of some sorts in pump or valve, loose wire, damaged insulation, something like that.

 

[Agile]

There are many possible causes but the pump is the most common.

To check/eliminate the pump then power it from a 13A socket with 3A fuse in the plug.

Tony

 

[ottosump]

Thanks for the advice guys, ran the pump over the last few days connected to the supply with a 3 amp plug as suggested. The system ran for an hour or so then blew, pump wall still running, ran the system with the thermostat turned off at the wall, the system blew again, pump again was still running. Followed your advice with regards to fitting a 3 amp fuse to the spur. Any advice on what to chek next would be appreciated.
Regards Otto

 

[Agile]

That has eliminated the pump.

The next most likely is a motor valve leaking water and causing arcing.

But after that it can be quite difficult to identify the problem as it can be almost anywhere.

As a last resort an in line 1A QB fuse in series with every mains supplied item would be a method which would eventually identify the problem.

You may be better getting a professional but if you persevere you should find it but you will have to be logical with your tests.

Tony

 

[bengasman]

Any advice on what to chek next would be appreciated.

Short of some sorts in pump or valve, loose wire, damaged insulation, something like that.

 

[Agile]

My post above about putting a fuse in series with components was intended to be read as putting a fuse in each circuit in turn rather than fitting 10 fuses all at the same time.

Of course either method would work and 10 fuses would achieve the result quickly.

Tony

 

[ottosump]

Update for the above, I have ran the system now with the Motor, Diverter valve and the thermostat on the hot water cylinder disconnected. Did notice yesterday that when the fuse blew, a spark jumped out of the timer switch ( Randall 103 mechanical timer) with the help of a couple of guys on here I've managed to source a replacement. In the meantime can anyone advise as to whether there is a simple test to do to eliminate the timer from the system as faulty before I purchase, they are quite expensive.
Regards Otto

 

[jaysean1]

can you isolate the system and leave just the timer connected, try taking out the cables to the heating and the hot water one at a time and or both at once.
hope this makes sense as I am a electrician not a plumber

 

[bengasman]

...can anyone advise as to whether there is a simple test to do to eliminate the timer from the system as faulty before I purchase, they are quite expensive.
Regards Otto

An independent 2-channel Honeywell ( which is infinitely better than what you have now ) is about £70 incl vat; not what you call expensive.

 

[Agile]

Some people would think thats expensive compared with say £10 for a used and outdated 103 !

Tony

 

[ottosump]

It is rather expensive, a new mechanical 103 costs approx 40-50 pounds, I don't need anything fancy. Its for my daughters home, she is out of the house at work most of the day so the dual programming is sufficient for her needs.
Regards Otto

 

[bengasman]

The extra 20 quid will give her a significant boost in performance for both ch and dhw.

 

[MeldrewsMate]

Hello group, I'm currently having bother with a gravity fed central heating system.

Diverter valve and the thermostat on the hot water cylinder disconnected.

These statements are almost certainly contradictory. Let's assume you really meant you have a fully pumped central heating system...

1. Water in the timer from a leak elsewhere?
2. Loose terminal inside timer?
3. Yes, you can operate the system without the timer, by joining together the wires switched by the timer (it is, after all, just an automated switch). This will eliminate or comfirm the timer. You'll need someone competant with electrics for this, it's not easy or safe to do it by letter!
4. Is the diverter (3-port) valve leaking, and wetting the internal switches?

To blow a 13A fuse will seriously expose your wiring to a fire risk, so stick with the 3A, and don't be tempted to revert to a larger size!

5. Insulation breaking down in the pump windings, usually causes almost instantaneous fuse failure (strictly speaking, the fuse hasn't failed; it's done exactly what it's meant to do!), and you've already eliminated the pump as a failure point.

6. Once had the gas valve coil insulation on a Potty Suprima occasionally break-down on fire-up. It's a long shot, but you can test for that sort of thing by turning the boiler thermostat up and down repeatedly, and seeing if the fuse blows on gas valve switch-on, indicated by an audible click from it - ITT gas valve now replaced with Honeywell as a repair kit from Glowworm.

MM

MM