C/H pump not working unless HW is switched off

[masonmjs]

My system comprises a Kingspan 180L unvented hot water tank, Danfoss FP715si controller and a Bosch Worcester Greenstar Ri boiler, which works perfectly as far as I can see (and is serviced by BG every year).

The problem is that the CH pump will only start if I switch the HW to manual, if they both come on together (as programmed) the CH pump will not run with the HW on. The system uses a Center EHE0200157/U 22mm three-port, mid-position valve.

This problem started shortly after a new tank (as above) was fitted and actually did operate OK for a week or two but then it started to go wrong. Initially both CH and HW would come on OK but the CH would stop circulating after around 2 hours running and would only work if I switched HW to manual as above, now it won't even allow the CH pump to start.

HW is only heated via the boiler, I have not connected the immersion heater so it is not part of the problem and can be ruled out.

Can anyone suggest what could be wrong and how to check it please (I am a control systems engineer by discipline so hopefully I can follow guidance and test as appropriate).

Thanks in advance.

 

[Murdoch]

Why aren’t you getting the installer back?

 

[Aquarius]

By hot water set to manual, do you mean latching the 3 port into manual?

 

[masonmjs]

Hi,

No I mean by pressing the manual button (for HW only) on the Danfoss programmer, it switches the HW off and the CH pump then starts and circulates.

 

[masonmjs]

Why aren’t you getting the installer back?

I'm not truly convinced it was anything he did, it was working to start with after all, and only started to have this fault around 2 weeks afterwards. The other reason is that I can't get him to communicate with me now, he left without giving me an installation certificate (it's an unvented tank), he promised to post it and has not done so. I'm not even convinced he was certified to install the tank as I have checked around a few of the biggest training companies and he is not registered with any of them. It is certainly the last time I will be using MyJobQuote to find a tradesman as they don't even ask for proof of certification as far as I can see. (I was also stupid on that front and didn't ask to see it).

 

[masonmjs]

By hot water set to manual, do you mean latching the 3 port into manual?

Hi,

No I mean by pressing the manual button (for HW only) on the Danfoss programmer, it switches the HW off and the CH pump then starts and circulates.

 

[masonmjs]

Can anyone help with this problem, just a few pointers would help, it has worked since the tank was installed but it only works sometimes now with the CH and HW programmed to come on together. The HW seems to take control and stop the CH circulating.

I am working around it just now by switching the heating and the HW on at different times but that is not likely to be good for the wallet I surmise.

Please help if you can ...

Thanks and Merry Christmas

 

[Stu-B]

I thought 3 ports on unvented weren’t allowed, it’s got to be 2 2ports and an auto bypass.
it’s to do with the dhw port being open when off that can overheat the tank.
you need to get your installer back to change it
That’s basics, god knows what else he’s done

 

[SJB060685]

I thought 3 ports on unvented weren’t allowed, it’s got to be 2 2ports and an auto bypass.
it’s to do with the dhw port being open when off that can overheat the tank.
you need to get your installer back to change it
That’s basics, god knows what else he’s done

Three ports are allowed on unvented but need an additional 2 port downstream.

 

[SJB060685]

Here you go buddy