Of boilers...

[MattG]

So the new boiler is in, which is nice. Somewhat warmer too.

Unfortunately, there is a slight problem. The boiler happily runs, as does the pump and the valves, the radiators warm up, and once the water returning to the boiler is at temp, the boiler cuts out, as would be expected. However, once the water temp drops again, the boiler refuses to cut back in. If I turn off the power supply to the boiler for a few seconds, then turn it back on, then it fires away quite happily, until the water is up to temp, upon which it turns off again.

Which is annoying. Anyway, it's a Ferroli Sigma boiler.

Any suggestions, preferably ones that don't involve getting someone in, as no-one wants to.

[BigWallop]

I think you should leave it to settle down by itself for a month or so.

[Velvet]

Um, you're seriously suggesting the OP lives with his boiler heating the CH for just a one-time short duration before needing re-setting is feasible for a month? Just what arcane magic powers a boiler that will 'settle down' over that month?

Velvet

[Set Square]

It sounds to me that the over-heat stat is being tripped when the pump stops - and that turning the boiler off and on again resets it.

How is the pump being powered? Is it being switched off by the room stat along with the boiler - or is it connected directly to the boiler and controlled by the boiler's pump over-run stat? This could be critical - particularly if you have replaced a boiler which didn't need an pump over-run facility with one which does! Also, if the pump does over-run, the water must have somewhere to go - even if all the zone valves are closed - so that it can cool the boiler down. Depending upon the configuration of the system, a by-pass circuit may be required.

Can you tell us a bit more about the system - do you have a mid-position

3-port valve or 2 separate 2-port valves to control the HW and CH circuits? Is there a room stat? How many of the radiators are fitted with TRVs?

[spam]

There are two separate motorised valves controlling the HW and CH, there is no room stat, all the rads have TRV's, and there is a pressure bypass. The pump is connected to the return from the motorised valves, so that as long as either the HW or CH is timed to be on, the pump runs.

The boiler gets the water up to temp, then cuts out, as expected. The water continues to circulate through the system, and gradually cools down. At the point, with the valves open and the pump running the boiler shout fire again, but it doesn't.

Any suggestions on what to look at next?

Actually, thinking about it, the boiler has a switched set up for either fully pumped or gravity/pumped. The fully pumped having the pump wired to the boiler, presumably with overrun and such. When I get back home I shall investigate this further.

Thanks,

-- Matt@work

[Set Square]

Since the boiler is capable of being used in a gravity hot water system, it must be able to cope with little or no flow without overheating - so forget what I said earlier about pump over-run.

If your system has been designed to meet the latest energy efficiency regs - and if it doesn't have a room stat - it should have some other sort of interlock which turns the boiler off when all the heating demands are satisfied. This could possibly be in the form of a flow or pressure switch which senses that there is flow through the auto by-pass loop. A possibility is that - once opened - the by-pass loop is not closing again when one or more TRVs open. If this is the case, the flow sensor would continue to tell the boiler not to bother - which would explain your symptoms.

[MattG]

Ta, there is a pressure by pass which (I deduce) allows water to continue to flow when the TRVs are closed. I think that this was set incorrectly, so that the water was flowing through there. I've changed that, and we *seem* to be working ok. Which is nice.

Anyway, fingers crossed and I shall monitor the situation.

[BillR]

Shouldn't the switch contacts from the zone valves operate the boiler through its demand contacts and the pump should be fed from the boiler terminals provided for that purpose?

[MattG]

Well, from what I can make of the wiring diagrams I have here, the boiler and pump should both run from the zone value switch return, and the pump return is via the pump connections on the boiler.

That's with the boiler set to "gravity", if set to "pumped", then the pump live, return and earth all connect to the boiler. I shall investigate moving the boiler power feed from a permanent switched live, to the return from the valve switches.