Baxi Solo Problem

oh and how do I stop my email address being visible to everyone (I'm accessing via Google Groups) :( Too late now I suppose (It's not my main account anyway)

Mark

If your Baxi Solo is like mine, the pump over-run is controlled by the main thermostat - with an extra set of change-over contacts. When the boiler is below stat temperature, the pump is connected to switched live - so only runs when there is a demand from the room stat/zone valve or whatever. When the boiler is above stat temperature, the pump is connected to permanent live - so it runs for as long as it takes to cool the boiler down - rather than for a fixed time.

It sounds to me as if your system has never been wired correctly. The boiler needs a permanent live from the heating system FCU, and a switched live from volt-free contacts in the zone valves, (which are all connected in parallel). The pump must be connected ONLY to the boiler's pump connection.

It also sounds as if you have compounded the problem by fitting a pipe stat. If you implement a pump over-run with a pipe stat, it *must* have changeover-contacts - with COM connected to the pump (and no other pump connection) NC connected to boiler switched live and NO to permanent live. Any other arrangement will probably bring the boiler on when the pump is running in over-run mode - which is what you appear to have.

I'll take out the Pipe Stat. I think the COM/NC/NO arrangement is how I have it but who knows it was done in a bit of a rush while wife and weans were out.

So, the best course of action is to replace the boiler thermostat first, see if that fixes my all my problems, failing that check out the original wiring? I know that sounds obvious but I'm looking for minimum disruption. (I can do without the HW side- immerser and electric shower

- but not the CH side at this time of year) Any good, i.e. cheap, suppliers of Baxi parts?

Mark

Why do the think that the boiler stat is faulty. Does it turn the burner on and off ok to control the output temperature? The pump is controlled by an additional set of contacts within the *same* thermostat - so just that additional set would have to be faulty. Possible but unlikely.

My guess - as I said before - is that it's never been connected up properly. Sort that, and it will probably work!

If you do need spares, have a word with Geoff at

The pump should be connected to the pump terminals on the boiler. Sometime the installers simply put the pump in parallel with the boiler demand.

No good reason other than following the fault finding diagram has a branch that suggests that you can have an operational (ie controls temperature) thermostat but the pump does not overrun. The solution they give for this is to replace the thermostat.

I take on board what you say though. And if fixing the wiring sorts it out then I have the cheapest solution of all!

I've found a supplier of what I think is the replacement thermostat (it seems to have been superceded by a newer model) and it's only =A318 so not the end of the world anyway but thanks for the link. I'll file it for future reference.=20

Mark

Yes, but the fault-finding chart assumes that it has been installed correctly and has subsequently gone wrong. It sounds as if yours has *never* worked properly. As Ed has suggested, the pump is probably connected to the switched live and not to the specific pump terminals.

As I said earlier, the boiler needs a switched live *and* a permanent live. Without a permanent live, pump over-run won't work - because the pump needs a source of supply whenever the boiler demand has been removed but the boiler is still too hot. So check *all* the wiring.

Fairy nuff, I think that is what I was saying I would do but maybe I missed out the check wiring *first* then go looking for other problems. It's unlikely I'll get a chance to look at it before the weekend so I'll post an update after that. I think my first task will be to label the mess of cables in situ before trying to rearrange them. I'm generally a messy bugger but I like wiring to be neat with nice diagram beside it to show what's going on.

Mark.

In message , pollocmc writes

Cease posting ?

In message , Set Square writes

reasonably common fault. The Solo mk 1 has a much more primitive pcb and doesn't control the pump

I assume you mean that the *PCB* doesn't control the pump on the Mk I?

The *boiler* still controls the pump via an extra change-over contact on the main stat which connects the pump either to switched live or permanent live depending on whether the water temperature is below or above the stat setting.

In message , Set Square writes

Yes - in other words, I wouldn't be able to help by sending him a PCB

I was pretty sure that was what you meant, but felt that "The Solo Mk I . . . doesn't control the pump" could be misinterpreted by some people.