CH/DHW - A Dogs Dinner

[Harry Beedlebow]

Hi all,

Recently moved into new home (Bungalow) and have been racking my head with the current CH/DHW setup - Sorry for the long description...
Boiler: Vissemann 100W 2-Pipe config
Setup: Standard Boiler and DHW Tank, driven (I thought) by a Danfoss 102E7 programmer and linked with a classic Honeywell analogue wall mounter stat.

Primary observations:
- No Tank stat fitted
- Only x1 actuated valve - a 2-port Drayton ZA5
- 2-Port valve located after inlet to DHW tank (see image).
- Only L, N & E cables are connected - Orange & Grey are terminated (well they have a bit of red electrical tape on them!)
- Other than L, N & E, there are NO other external connections to the boiler (Boiler is in garage with ample visible room around it and no other cables coming to it and nothing connected to the signal ports internally when boiler casing opened). See image of boiler connections where L N & E are in and ports 96 are bridged with no comms attached.

Operation as I see it (and after chasing through the loft)
- Boiler heats up the DHW tank at all times - there's nothing to tell the boiler to stop running as far as I can see - with no tank stat and no connection to boiler
- When CH is required, Danfoss unit kicks in and puts power directly on to the 2-Port valve
- Valve opens and lets the (already flowing to DHW tank) water through to the rads network.
- When temp is achieved, Honeywell stat cuts power feed to the Danfoss and in turn the 2-port valve - closing valve on spring return and cutting off CH water flow.
- DHW tank remains running.
- Extra bit - every time CH goes off there's a clunking noise - I've traced that back to the 2-Port valve as it looks lie its been piped up in reverse so flowing into B and out of A!
- I can get the house warm and I can get hot water but this really doesn't look or feel at all logical or right to me.....

Some Questions I would love your input on:
1. Has anyone come across a setup like this before and if so - any ideas of its point (if there is one)
2. Can a boiler manage the process locally if it has no external command feed i.e. I've heard theories that it can sample local water temp and make a rudimentary decision to switch on/off based on the results.
3. Am I missing something here based on the above? Should I be looking elsewhere for a mystical second 2-port valve.
4. I obviously intend to re-vamp the current process - my thoughts were to shift it to S-Plan versus Y-Plan - any thoughts/advice on which and why?

Really looking forward to hearing peoples thoughts and opinions on this one - Thanks in advance

 

[CBW]

It does seem bodged, but could have been a gravity system. I would personally go with S plan system.

 

[Harry Bloomfield]

- I can get the house warm and I can get hot water but this really doesn't look or feel at all logical or right to me.....

I have seen even more rudimentary systems than that. It looks as if the 2-port was added some time after the rest of the system. Even systems where the only way to enable/disable CH, was via a manual valve, with HW enable whenever the boiler ran.

Look at converting what you have, to an S-plan. Adding a valve to the HW and a stat to the cylinder.

Add a timer to both HW and CH, plus a room stat - you will then have a reasonable system.

 

[Harry Beedlebow]

Looks like S-Plan is going to be the way to go - at least then I can get the boiler a little more under control than it currently is - I still can't get my head around a zero signal connection to the Boiler, very inefficient.

 

[stem]

My parents bought a new build bungalow one of a development of 30 or so back in 1980 and that is how their system was originally installed. The Hot water channel of the programmer controlled the boiler and pump. There was no cylinder thermostat and they both ran continually when the HW was selected to be on.

When heating was selected, it opened the motorised valve (via a room thermostat) and the radiators came on. Because of the arrangement, it meant that the HW had to be 'on' in order for the boiler to work, so the programmer was set to 'gravity' operation which automatically turned the HW 'on' when the CH was selected to be 'on'.

My father was a plumber and I was at college studying electrical engineering, so, the following year, between us we added a second motorised valve for the HW to convert it to an 'S-Plan'. However, the original CH motorised valve didn't have a switch inside to control the boiler, so I had to add a relay to perform this function.

 

[Harry Beedlebow]

stem: you have described our situation practically word for word - especially the 1980's build (ours is 1981) - I'll be converting to S-Plan and changing out the current hardware - CH 2-Port is piped in reverse which gives a nice unique clunking noise when CH is no longer required and so its x2 new valves (with internal switch), assign a comms feed to the boiler so it can actually be told what to do and upgrade the control logic to something a bit more digital and WiFi-ish (thinking a NEST or Ecobee)

 

[stem]

stem: you have described our situation practically word for word - especially the 1980's build (ours is 1981)

I hope you didn't inherit the 8mm microbore for the radiators as well.