Combi boiler nightmare

Affynity

Not sure if anybody can help me out here, who may have had this issue and resolved it somehow.

I bought a house a month ago and the boiler, serviced by the seller 10/05/17 and allegedly in perfect working order, has this bizarre habit of just heating up water for no reason, and for hours on end.
When it's in this apparent state of madness, the central heating will not switch on.
I had a serviceman come check it out, he replaced the diverter, fixed a leak and apparently deactivated its eco mode. But without fail, it will always go back to this bizarre period of killing the central heating to heat up water for nobody's use.

For reference, its the Baxi Main Eco Combi Boiler. I don't have a thermostat, I've disabled the timer function for selective automatic start up, I've kept the selector switched to hot water and central heating (opposed to hot water only) and I've turned the hot water temperature all the way down to disable intelligent auto pre-heat.

Literally at my wits end, as I'm wiped out from buying the house and I've only been here since 02/06/17. I'm worried in winter I'm going to have heating that kbky works if the boiler is in a good mood.
I did try contacting the seller's serviceman but they literally sound ultra dodgy.

I_have_spoken

Are you sure it's a combi - do you have a HW tank? Could by a faulty HW flow sensor that is triggering. Doesn't the boiler shut down with an over-temp warning?

Without an external thermostat override, the boiler may not reckon CH is needed in summer temps so won't come on.

Browntoa

I've got a mega flow hot water tank in an upstairs cupboard , the heating comes on to heat domestic hot water on its own .

It looks like an immersion and has an option to heat like a traditional one by turning on the electric via a switch next to it

Alex1983

If you have a mega flow you probably have a system boiler not a combi, have a look under the boiler and see how many pipes are there, I would guess it will be 3 which will make it a system boiler.

Your fault I would think will have to be a faulty zone valve, which is stuck open causing the hot water to stay on continuously. I know you said you've had a diverter vavle replaced, was that at the boiler or the airing cupboard?

timjim

Alex, the OP is not the poster who mentioned the mega flow, but some else who's just added a confusing comment

Alex1983

Ah I see, getting confused by the different posts.

So when you say it's heating water, is it heating the radiators up. Maybe a sensor that's acting as a frost stat that thinks it's very cold and running heating. If it's not heating the radiators then does it over heat or just cycle on and off, does the dhw light stay on, as suggested maybe hot water switch stuck or sticking intermittently.

Affynity

Its definitely a combi.
The service people must have missed something because its literally trying to maintain the hot water temperature constantly, almost like there's a hot water user in the house that I don't know about.
So, in winter i won't be able to turn on the central heating, in summer, the upstairs is tropical because the boiler is constantly hot
The system's documentation is useless. It has a reset switch that doesn't seem to do anything. You use it and no sounds, lights or number values seem to change.
The seller of this house has clearly sold me a dud

I_have_spoken

Best get the repair people back in

Affynity

Alex1983 wrote: »

Ah I see, getting confused by the different posts.

So when you say it's heating water, is it heating the radiators up. Maybe a sensor that's acting as a frost stat that thinks it's very cold and running heating. If it's not heating the radiators then does it over heat or just cycle on and off, does the dhw light stay on, as suggested maybe hot water switch stuck or sticking intermittently.

The selector is constantly on hw and ch, the only other options I have is hw only or off. I turned the hw temperature to minimum, which apparently kills the preheat function.
If I want the ch on, there's a timer switch that has off/on/selected timed start options. So i leave it off and just turn the ch on when I feel the need

Currently, all I have is a reading of 62 (I'm assuming thats the temperature), the hw light is lit (nobody is using hot water) and the pressure is 2 bar.

That's literally my entire function with this boiler. When the hot water light turns off, then I could turn on the heating, but I have no idea how to influence that.

I_have_spoken

Guides to using the Baxi - http://www.baxi.co.uk/gas-boilers/discontinued-products/the-baxi-maineco-range-has-been-dicontinued.htm

Affynity

I_have_spoken wrote: »

Guides to using the Baxi - http://www.baxi.co.uk/gas-boilers/discontinued-products/the-baxi-maineco-range-has-been-dicontinued.htm

Never reassuring to see your boiler in the manufacturers obituaries...