Boiler upper limit switch from where?

[T i m]

Hi all,

I believe I need an upper limit switch for an old but until today, 'trust' New World / Ascot CH502 (G.C. No. 41-620-30)balanced flue boiler.

The switch itself seem to test out ok on the bench but the boiler won't fire up with it in circuit. I did get it to fire up with the switch tacked on externally but when I gave it a slight tap the boiler closed down (possibly going higher when under load?).

It's possible the boiler may have got warmer than usual for a few seconds as there appeared to be an airlock (old gravity system that was partly upgraded years ago) and the switch did need resetting (so the likely cause isn't unknown as such).

It's the long copper probe type and in case it helps it is marked:

On the tin: P7638 -- LM5 -- 388312P

On the actual switch body: Ranco -- Type L -- T100 -- MR2

I've had a quick Google about and not had any luck (and it's too late to phone) so I wondered if any kind soul could point me in the right direction please. We only need to get the boiler going (safely) till phase 2 of Mums project. ;-)

Cheers and thanks for your time etc.

T i m

[geoff]

In message , T i m writes

Then the contacts on the bi-metallic strip prolly gone

Are these stats not pretty generic?

One of the old farts in diynot might be better able to help than us sprightly young coves that post here

[T i m]

Hi Geoff,

Funnily I thought of you when I first pinned it down to this switch. ;-)

I had thought of trying a couple of things.

1) Drilling a tiny hole in the case of the plastic switch body (say 1mm) and spraying some contact cleaner in there and giving the switch a good workout (you can open the contacts by pulling the reset button against a spring) or 2), opening (Dremelling off?) the crimp around the tin, opening it up and cleaning the contacts and re-epoxying it together?

I would have thought so but I don't think they are used any more. I do have a Plumb Centre near me and although I normally only go there as a last resort (service is slow and prices aren't cheap) they can / do have the database lookups.

Ok , not used them as yet but it might be worth a go. Luckily Mum doesn't need the heating atm and has the immersion for her hot water so it's not desperate desperate.

Cheers, T i m

p.s. I think she is of the opinion that using the immersion is going to be 'very expensive' when compared with an old balanced flue boiler? What do you reckon please? (I'm not sure there would be much if anything in it)?

[Roger Mills]

I guess they're all fairly similar - though not necessarily identical.

On my 20-y-o Baxi Solo, the overheat stat has a very thin bulb which fits inside a cut-out in the main stat's bulb - so that they both slide into the heat exchanger pocket together.

My overheat stat is a Ranco LM7P8505 - which is still avaailable from various online sources. Dunno whether it would fit the OPs' boiler.

[Roger Mills]

If she can run the immersion heater from an off-peak supply, that will probably be cheaper than gas.

But peak electricity is 3 or 4 times as expensive as gas per kWHr, so the boiler doesn't have to be that efficient for gas to be cheaper.

[T i m]

On this 'Ascot' the overheat stat fit's in it's own pocket / tube running just under the top line of the fins inside the heat exchanger.

Thanks for the suggestion but the 'bulb' would be too large a diameter for this installation. I should have included some pictures earlier:

tube is about 50cm long and 2mm in diameter. I could be 10" long though and could be mounted anyhow.

The location seems the best to me as I'm assuming it would give the quickest response to an overheat situation? What if there was no water in the boiler at all and the overheat stat was in the flow pocket with the main stat (like the stat is on this Ascot, although there may be two stat 'tubes' going in there on this one)?

Cheers, T i m

[T i m]

Ah, thanks for that Roger. Only single tariff for her I think.

Cheers, T i m

[geoff]

In message , T i m writes

Just take it in to HRPC (partcenter) or somewhere and ask them if they have one like it