c/heating cuts out & stays out - 3 port valve problem?

BACKGROUND

Hi, I have this last week had someone in to install a thermostat on my hot water cylinder (it didn't previously have one) and a 3 port valve (I don't pretend to understand what this is for, but the problem it was aimed at fixing was the virtually constant overflow of very hot water from my hot water cylinder into the attic hot water tank.) In the past couple of months I have also had a new radiator fitted and been powerflushed but I doubt that would have any impact.

The main components involved are:

Baxi Solo 2 RF gas boiler (regularly serviced and pilot light still on)
Salus MV322 3 port motorised valve
Honeywell L641A cylinder thermostat set between 50 and 60 degrees

THE CURRENT PROBLEM

Two days after the valve and thermostat were fitted, my central heating has suddenly stopped working. It was going nicely all day, then cut out before the programmed time this evening.

I did a manual override to switch the timer off, then switched it back on and it came back to life and worked fine for about another hour.

It then cut out again and has since refused to come on at all. Absolutely nothing happens when the timer is switched on - usually there are a few clunks and groans and the boiler fires up and the whole system gets going, but now there is just the loud silence of absolutely nothing happening!

OPTIONS

I have three options - try fix it myself (my preferred option, given that it's the weekend and freezing cold, but only realistic if it's something really easy like a switch!), call back the engineer who fitted the thermostat & 3 port valve, or call out a British Gas engineer under the terms of my maintenance contract.

To help me decide which is the best course of action, I'd like to know is whether there is likely to be any connection between the installation of the 3 port valve thingie and the heating being on strike? Also, can anyone explain in words of one syllable what the 3 port valve actually does?

Would greatly appreciate any help - thanks very much.

(Incidentally, with the hot water cylinder set at 65 degrees, the water is still overflowing into the attic tank and the water in that tank was still quite warm earlier today - although not as hot as previously, I would presume it shouldn't be routinely overflowing at that temperature?)

With the hot water on and the boiler firing, you should be able to get the heating working by operating the manual actuator on the motorised valve.

However, if / when the cylinder reaches temperature everything will shut down - so this is just a temporary workaround.

Get the installers back asap, it's their responsibility.

Well Sir, the 3way valve should now "talk" to your heating system.
With your new cylinder stat in place about 1/3 from the bottom of the cylinder and set to a max of 60f, as the stat calls for hot water heating, it asks the boiler to run and also the 3way valve to open to let the heated water from the boiler now go to heat the hot water cylinder.
Your man, i think would needed to drain your system down to allow him to fit the new 3way valve and there is now a good chance that the system may have:
1. air lock
2.fuse may have blown if as you say Absolutely nuffin happening
3.new electrical connections failed
4.does your boiler have a reset button?
Once the hot water in the cylinder gets to setting set on new stat it asks the 3way valve to shut the heating water off to the cylinder, the boiler now stops or if still on timer/programmer allows the heating water to flow via the 3way valve but to the rads only.
Try bleeding your system to start with, give it a good bleed not just a quick one.
If you still are getting hot water in your header tank,try lowering the new stat to say 55f if that does not work, maybe a hole in the cylinder coil......thats me done,off to bed!

Thanks, guys, for your responses. I have an update...

Much to my surprise, the heating sprang into life at 05:30 this morning (per the timer). It's set to stay on until tonight, but by 08:30 it has cut out again. So it's perfectly capable of working, but it just doesn't seem to want to.

With my noddy level of knowledge that would seem to rule out the airlock, blown fuse, and failed connections. Have tried the boiler overheat reset option but it made no difference. Also, I've tried switching the 3 port valve to "manual" (as opposed to "auto") but it makes no difference.

Have tried bleeding a few radiators but they just dribble out water - I think it might need the pump to be working to bleed 'em properly.

Off to have a shower before the air temperature drops any further!

From what you are now saying, looks like the new 3way valve maybe wired-up wrong. Bet if you run off some hot water your ch comes on to replace the used hot water. If this does happen you could IF your hot water cylinder has a flow reducing valve in line, part close it to make the hot water flow from the boiler to the hot water cylinder take longer to reheat the used to water, thus keeping the boiler and the ch on longer.

Which programmer/timer do you have?

When you say that the water in the loft tank is getting warm, do you mean the large tank or the small tank?