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[I_want_an_Omega]

Ok, what I call a standard central heating system.

Conventional (condensing, but non-combi) boiler) followed by the pump feeding a couple of motorized valves, DHW tank, rads etc ......

For a few week or so I've been having an earth trip - sometimes days apart, other times hours - reset the breaker and all is then ok. It's taken a while to pin down which circuit it is - but have now proven that it's the boiler - which is on it's own MCB. However, this morning the fault has gone hard and consequently the heating is off. SWMBO not happy.

Other symptoms were that the DHW system was coming on all by itself even when controls say it should be off - so, this seems to point to a failing motorized valve. DHW then turns off when the tank-stat gets to temp. I discussed this with the controls people (Horstmann) helpdesk who say this is a common failure mode and symptomatic of a failing valve - and to confirm by removing the controller from the wall (its a multi-pin plug in). The DHW fault remained, which they said proved it was a faulty valve and that the controls were ok.

My idea is to totally disconnect (electrically) the suspect valve. I's see this as a temp fix - prior to replacing the valve. The location of the valve isn't good, so I want to get the heating going first and then get a plan in place to replace the valve - may even locating it to somewhere more accessible. The valves are 15 years old and have non-removable heads.

Ok, downside is no DHW, but can use the immersion on a temp basis and would get the heating going again.

Comments please guys .....

Thanks - Rob

[Kevin Wood]

If you have an RCD tripping, then you have earth leakage somewhere in the system. You need to find this first. I suppose it may be the faulty valve, but it won't necessarily be related. I suppose if water had leaked into the motor housing it might.

Disconnecting the valve could be a good way to eliminate it. If, as it sounds, it has stuck in the open position, you might still end up with hot water in abundance, as it will heat whenever the heating brings the boiler on!

If the RCD still trips, you have another problem somewhere in the system. Often the immersion heater is on the same circuit as the boiler controls, and this is the component I'd reckon would be most likely to suffer a fault to earth.

[TheBoy]

As said, usually a valve, probably the gas valve (can't think of others in boiler). Easy enough to replace, but care must be used if it is the gas valve, obviously.

[TheBoy]

Soz, misread, you've proved to 3 way valve or zone valves? So external to boiler? In which case you have found fault.

Easy change, partial draining needed

[TheBoy]

Should add, when I bought my first house, my lodger, dozy bint, washed a duvet in the bath and dried it in the airing cupboard, and it dripped on 3 way valve. Fault started out by heating going mental (in the summer), and the bath being freezing. Then it started popping the trip.

In that case, as the valve itself was fairly new (it was a new build), I just replaced the electrical/motor bit, not the mechanical valve, hence saving the drain down.

If the valve is older than 5 years, I'd replace the entire valve.  Remember to put inhibitor in after fitting - I use 2 bottles of the ShitFix own brand stuff when I do mine.

[I_want_an_Omega]

Thanks chaps.

There are two 2-port valves as opposed to a single 3-porter.

Immersion is on its own circuit from the main board.

Off to try things now - so will keep you posted.

Regards - Rob

[I_want_an_Omega]

Ok, update.

Disconnected the DHW valve and powered the system up. Heating now doing what it should.

Half an hour later, TRIP. Grrrrrrr

Next idea is to isolate the other valve on the heating circuit and see if that's the culprit.

Not much left really, boiler and pump. The good news is that the boiler is still under warranty, but there isn't really any way of testing one without the other ..........

Grrrrrr ...............

[YZ250]

Soz, misread, you've proved to 3 way valve or zone valves? So external to boiler? In which case you have found fault.

Easy change, partial draining needed

On a side note, if it's a gravity system with a feed and expansion header tank in the loft, you can 'bung' these two pipes to save draining down. I've worked on mine with 'live' water many times. This doesn't help with the trip problem though sadly.
Obviously limit the amount of open pipes to two though, unless other pipes have isolators on them.

[I_want_an_Omega]

Did a reset after the trip and it's still working - for now.

SWMBO wants it left on to warm the place through for a bit - which seems reasonable, so further diagnostics on-hold for a bit.

The other good news is that my heating chap has been in touch - so will be having a chat with him shortly.