central heating fault: fuse blown - pump?

[Stephen]

Hello,

I went away for a couple of weeks and I didn't know how cold the house would get so rather than turn off the heating, I left it set low for frost protection so I didn't come back to burst pipes. When I got back, the house was very cold and the boiler was dead. I investigated with a volt stick and found that current was going to the boiler from the FCU but no further. I looked on the PCB and there is a 1.6A fuse that had blown. I didn't have any replacements: the best I had was a couple of 1A fuses from a shaver socket adaptor. The boiler tries to start but there is a funny noise and then the fuse blows. It doesn't help that I was using 1A fuses rather than 1.6A.

I only got a second or two before the fuse blew, but I think the noise came from the pump. Would that make sense? I've read that pumps can seize. If it was seized, would it stall a draw a higer current than usual and blow the fuse? I read that you can unscrew the large screw onthe shaft of the pump and try to move the pump spindle. The boiler is an ancient Seme and I know I need to save up and replace it with a modern condensing boiler. The pump has a bolt head in the centre of the shaft which I managed to loosen and I could feel the shaft rotating but some black water came out.

I am waiting for some replacement fuses to arrive. I'm wondering whether the pump was seized and whether I have managed to loosen it. Do you think it is worth taking the pump off to give it a rinse? I was surprised the water that came out was so dark as I added inhibitor and a magnetic filter.

Do you think I should get a new pump just in case? The one fitted is probably the original and very old.

I read that sometimes valves stick when you go on holiday but as this is a combi boiler and the heating is on one zone, the only valve is the diverter that switches between CH and HW and since I get neither CH nor HW, I'm sure the problem lies somewhere else.

Thanks in advance!

[harry]

Look on the motor end of the pump. In the centre of the motor there may be a cap with a screw slot to remove/unscrew it. (There may be a little water gets out when taken off)

This gives access to the motor shaft which has another screwdriver slot which enables you to twiddle the shaft to free it up if it has seized.

[The Natural Philosopher]

The answer is yes. Most pumps have a central place where you can remove a cover with a slotted screwdriver and rotate the spindle by hand or using a tool. That can free up any crud enough to get the pump working again. Until you can source a new pump and go through the faff of draining down refitting adding the fernox and then trying to get all the air out of the CH. I wish you luck.

[alan_m]

Pumps usually seize only if they have been left unused for a period of time such as in a system where the pump is only used for central heating and the heating has been turned off during the summer. A friend who was in the plumbing business used to get a lot of pump failure calls in Autumn when people tried their heating for the first time in 6 months.

Was your heating running OK before you went away. If so then maybe the fault is elsewhere - although a faulty pump cannot be ruled out.

The noise you are hearing may just be the normal pump noise on starting as the boiler fires up and you haven't noticed it before because the noise is normally of short duration before the burners fire up. If as you say the shaft is turning then it is no longer seized (if it had been in the first place). A small amount of water with the pump screw cover removed is normal and its colour is more of a indication of the sludge etc. in the system (or had been in the system) but probably at this time not the cause of your failure.

If you have the necessary competence disconnect the pump wiring and apply mains voltage to the pump from another source and if you feel it running and/or see the shaft turning then the pump is possibly OK. Google also for central heating pump starting capacitor. Do not attempt to fire up the boiler during this test.

Do you have an installation manual for your boiler, or is there one on the internet (installation manual rather than a user guide). It may have a circuit showing what the fuse is protecting and/or a fault finding step by step flow chart.

[tabbypurr]

Pumps can seize, and yes undoing the centre screw is sometimes enough to free them. Gunky water is normal. I'd disconnect the pump & fire the system up, but only for several seconds as the boiler will get no flow & overheat very quickly. Then you'll know if the pump is the problem.

NT

[Thomas Prufer]

Yes...

Possibly.

Yes.

If it was stuck, it isn't now...

If it was, it isn't now...

No.

Depends -- on when you replace the boiler, and the risk of another pump failure. If the pipes freeze, that's bad, if the house goes a bit cold and you need to use electric heaters or a woodburner for a while, it's not.

Thomas Prufer

[Stephen]

Hello,

Thanks for all the replies.

The pump is only used for CH. I had the CH thermostat turned dwen low for frost protection, so I don't know how often the boiler fired up while I was away. I must have fired at least once to blow the fuse.

I never thought to power the pump independently, thyatnks for that, I'll try that if there is ever a next time.

What limited me on the day was that I didn't have any 20mm fuses, other than a 1A one from a shaver adaptor and they are not very easy to find. I'm surprised at this because you would think they would be very popular in shaver adaptors, especially now everyone has electric toothbrushes, as well as shavers. I think office clocks still use BS646 fuses too.

I've managed to order some 1.6A fuses, so it's a maytter of trying them when they arrive.

The pump does not have the central screw. Instead it has a hex head bolt. I'm not sure if that's how it came or whether that's an "after market modification" by a previous owner/plumber, but it seems to do the same job. I couldn't remove it completely, but once I had loosed it, the shaft seemed to turn rather than the screw.

I suppose it wouldn't hurt to drain it and top it up with fresh inhibitor. I'm just not sure whether this was a warning that the pump is on its way out and whether to replace that at the same time.

[Thomas Prufer]

They do last multiple decades...

Thomas Prufer

[Jonathan]

I was once advised by a plumber's wife (to save the call out charge) to hit a seized pump with a hammer a few times. Did the job and it carried on working.

Jonathan

[The Natural Philosopher]

Ah. The old joke.

Customer objects to $100 bill for hitting the water pump with a spanner, so the bill is re-presented

"To hitting the water pump with a hammer -$1 "For coming out, knowing where to find it, and how hard and where to hit it - $99

TOTAL $100

[bert]

Preferably a rubber one.