Obscure heating system fault.

[Tim Lamb]

We were welcomed back from holiday by a cold house and defrosting freezer! Put early evening clockwise travel on the M25 into perspective.

Thank heavens for log burners:-)

Initial investigation found that the boiler system was tripping the 30ma RCD protecting the ring mains. Isolating the boiler got things running and we spent the evening sorting partly defrosted foodstuffs.

With the boiler fully disconnected (Potterton Profile 100E yes I know it is old and inefficient) the fault persisted. With the circulating pump isolated and the boiler reconnected the fault disappeared.

Eureka moment, the pump must be faulty I'll replace it with one of the two spares I have in the barn. Bit of furbishing with a wire brush and a check that the spindle rotates and in it goes. Ta-ra! Switch on and out pops the 3 Amp fuse! Duff capacitor? Change that. Now which terminals did the old one use? More fuses. Must be the motor, try the second back-up. More fuses.

About now I began to wonder if I had inadvertently swopped the two black wires (pump) when re-connecting the boiler wiring......

I have the *S* plan circuit diagram (wiki.diyfaq....) which largely agrees with what I am finding. Is there another diagram which would explain the two *pump* connections at the boiler? My system uses the bathroom radiators for bypass purposes so the pump runs on after the heat call is satisfied.

Of course hidden cable runs and Mice remain a consideration!

[John Rumm]

Powering up the pump on a bit of flex connected to a plug (with 3A) fuse may either eliminate or direct suspicion in this case. (if you can stick an ammeter in there as well - even better). That way you would know if its really the pump or the wiring.

If its looking like the wiring, then disconnecting from the boiler etc and buzzing out (possibly testing with an insulation resistance meter) would probably be my next step.

[Roger Chapman]

I junked my 1991 60e very recently, not because it had finally given up the ghost, but as part of a major reworking of my house. Unfortunately the installation instructions went out with last week's recycling and my useless memory is of no help. However the electrical bits from the boiler are still in a heap in the corner of the kitchen and I can't see anything there that looks like an alternative pump connection. The internal connections on the boiler connection block go:

(Pump) Live, neutral, Earth (Mains) switched live, neutral, live.

Of course the 100e might have been a bit more elaborate but without the destructions I just don't know.

Sorry I can't be more help.

[Tim Lamb]

Just tried that on one of the back-up pumps. Seems OK.

Yes. I am reluctant to disconnect the choc block wiring as it looks like the apprentice had a bad day. 2C+E with sleeving and dogs breakfast style. I suppose I could label stuff as it comes off. My Megger takes a PP9 battery so unlikely to work off the shelf.

If the original pump tests OK it has to be a wiring:-(

Probably quicker to renew than attempt a repair.

[Tim Lamb]

Ah! That might eliminate one possible error. My first two wires are black back to the fused spur back box where they join 2+E for the run up to the control box and pump.

I have the installation book which just refers to those two as *Pump*. The others are as you say.

[Tim Lamb]

In message , Tim Lamb writes

Later news.... the original Grundfoss Alpha 2 pump trips out the RCD on my workshop supply.

In view of the consequential cost, I might revert to a simple 3 speed pump and ditch the adaptive electronics.

I'll spend the evening doing a more careful check of the wiring and certainly *buzz* test the two black cables.

Meanwhile Google for Alpha 2 complaints!

[John Rumm]

That's a shame ;-)

Looking at the pump feed first would seem to be sensible.

All the normal wiring plans can be found here:

wiki.diyfaq.org.uk/index.php?title=Central_Heating_Controls_and_Zoning

[Tim Lamb]

OK John, found them.

My mistake was in disconnecting all the incoming connections to the boiler when fault finding. By re-connecting with normal colour convention, I put 230V on the boiler N and N on the line. Whether the boiler internals survive this sort of treatment is unknown to me.

For reasons only known to the original plumber, the whole system is reverse polarised. Sadly, the fused spur was clearly connected prior to installing the boiler housing and the worktop. Getting access to re-connect properly is going to be a pig and my brain can't handle fault finding blue cable running 230V!

The original fault was definitely the pump (some sort of earth leakage). New pump installed now but reverting to the original plumber polarities does not bring on the boiler.

Is there a safe connection I can try to test the boiler operation?

If I have to hurry over to Watford for a recon circuit board, I'd rather do it today than after a tedious rewire!

[Tim Lamb]

In message , Tim Lamb writes

OK. Scrub that. Linking live to boiler SWL brings on the boiler!

[John Rumm]

Depending on which contacts we are talking about - you may get away with it ;-)

Not exactly conducive to safe working going forward either...

Normally if you connect a loopback wire between the stat inputs on the boiler, it will run whenever powered on.

;-)

[Tim Lamb]

Jobs done:-)

Everything disconnected. Terminal blocks labelled. Re-wired as Wiki *S* plan + overrun. Doubtful cable colours buzzed through.

Fired up and operates normally. Huge relief!

Nothing on Google about earth faults on Alpha2 pumps.

Thanks for your interest and input.

[John Rumm]

Its nice when you beat a problem into submission by ruthlessly clubbing it to death with logic and method ;-)

Could just be water has crept past a seal somewhere.

Glad you got it working.

[Tim Lamb]

I opened up the pump electronics. Part filled with water as you say.

Cover retention is by snap in plastic loops but I suppose a determined repairer could use glue.

The design offers controls which imply motor current and flow measurement. Nevertheless, to site vulnerable components in a void only protected by a simple shaft seal verges on parsimony of a high order.

I suppose the circumstances of this breakdown might have been anticipated, holiday so no DHW use coupled with mild weather and CH turned down, leading to pump out of use for long periods.

Any value for the Wiki? Basically do not have freezers protected by the same RCD as electronic CH pumps.

[John Rumm]

Yup, its the kind of cost saving that does your reputation no good.

I think there are already comments in there on the designing with RCD sections.