Y Plan fault - damaging programmer

[PClem]

Hi,

I have a Y Plan system that has worked fine for years but recently developed a strange fault where the hot water on/off is only controlled by the Cylinder thermostat. The HW relay on the programmer is permanently on and although the relay clicks, its output does not change status with the indicator when selected.

System consists of:
Baxi Bermuda 45/4 Electronic Back Boiler
Drayton LP722 Programmer
Honeywell V4073A 3 way valve
Honeywell L641A Cylinder thermostat
Satchwell TLX 2259 Room thermostat

The wiring, following the Honeywell Sundial Y Plan diagram, has been double checked by another electrician and confirmed correct. I have replaced the Programmer, 3 way valve and cylinder thermostat. After replacing the programmer it worked correctly at first but the following day the HW fault had returned and it appears that something in the circuit is damaging the programmer HW relay.

By process of elimination I now suspect the boiler PCB – 237730 but would appreciate any suggestions or advice from those with experience of a similar fault.

Thanks in advance

Pete

 

[Leesparkykent]

Sounds strange. Out of interest has the pump been changed?

 

[buzzlightyear]

Poss wired wrong .

 

[Leesparkykent]

My thoughts...albeit a long shot it might be UPS2 pump and the suppression lead hasn’t been fitted.

GRUNDFOS 98525489 - UPS2 SUPRESSOR CABLE D21 | eBay - https://www.ebay.co.uk/itm/GRUNDFOS-98525489-UPS2-SUPRESSOR-CABLE-D21/332579770242?pageci=e576a34a-4896-4e20-a9dd-885adf9576f7&epid=1634668779

 

[Wilko]

Hi Pete and Welcome to the Forum
Just after some background - is this exactly the same programmer model that worked for years? Gravity fed?

 

[Wilko]

Here's a link to our brother Plumbers discussing the excessive startup current of this pump that LSK mentioned. I note the new programmer you've got doesn't have much contact current rating ...
Excessive current at Grundfos UPS2 heating pump start up - https://www.ukplumbersforums.co.uk/threads/excessive-current-at-grundfos-ups2-heating-pump-start-up.61979/

 

[PClem]

My thoughts...albeit a long shot it might be UPS2 pump and the suppression lead hasn’t been fitted.

GRUNDFOS 98525489 - UPS2 SUPRESSOR CABLE D21 | eBay - https://www.ebay.co.uk/itm/GRUNDFOS-98525489-UPS2-SUPRESSOR-CABLE-D21/332579770242?pageci=e576a34a-4896-4e20-a9dd-885adf9576f7&epid=1634668779

Thanks for this.
Forgot to mention that the pump was changed from a UPS 15-50 to a UPS2 so you may be on to something here. Thanks for the eBay link. Do you have a link anywhere giving details of when this suppresor cable should be used and what it prevents. Thanks again.

 

[Wilko]

Hi - I think they'd be looking to control the inrush current - if so would it likely have a negative temp coefficient thermistor in it. Just thinking out loud.

 

[Leesparkykent]

Thanks for this.
Forgot to mention that the pump was changed from a UPS 15-50 to a UPS2 so you may be on to something here. Thanks for the eBay link. Do you have a link anywhere giving details of when this suppresor cable should be used and what it prevents. Thanks again.

The lead comes with pump and should always be fitted.

 

[Octopus]

Sounds from reading the link thats what ruined the programmer.

 

[Leesparkykent]

I would fit the lead and change the programmer. I would bet this solves your problem.

 

[PClem]

Here's a link to our brother Plumbers discussing the excessive startup current of this pump that LSK mentioned. I note the new programmer you've got doesn't have much contact current rating ...
Excessive current at Grundfos UPS2 heating pump start up - https://www.ukplumbersforums.co.uk/threads/excessive-current-at-grundfos-ups2-heating-pump-start-up.61979/

Thanks for the input Wilko.
Programmer is the same type that has worked for years with no problem. System has always been fully pumped. Link you supplied makes sense where it talks about relay contacts welding together due to excessive current. Will get hold of the suppressor cables as suggested and may also check other programmers for higher contact ratings.
Thanks again. I had heard there were issues with the USP2 but didn't know any details.

 

[Leesparkykent]

I normally fit Honeywell ST9400C 2 channel programmers as standard...IIRC they have a 3A switch rating.

LMGTFY - http://bfy.tw/KhtW

 

[PClem]

Thanks for all the excellent advice.
I just wish I had posted here earlier !
Regards
Pete

 

[Chris halls]

Hi just found this post while doing a search for an issue I’m having. I litterallly have exactly the same issue with the programmer and have changed all the components except the pump and the boiler, the only difference is mine is taking out the micro switches in the 3port also. Previous there was no rcd protection in the property so I have upgraded it to a new rcbo board, thinking there might be a neutral/earth fault somewhere and that it would trip out the rcbo and I could narrow it down but no that didn’t work. The pump is a lowara ecocirc 25-4/130 not a grundos but it was a grundos about 6 years ago before everything was changed. Posted on another forum and most people were saying it was definitely the boiler. At my wits end with this job any help would be appreciated. TIA