Flow- Vent- Feed -Pump

[Madrab]

Why would you say that now that I have followed BS for OV!

When I say convoluted, that's not a bad thing or criticism, all I mean is the paths that the pipework takes to get to the rads, if I remember rightly, isn't one single 3/4" backbone loop with all the rads feeding from that? The 3/4" tees off at certainly points and heads in several different directions to feed rads in different 'zones'? That can make balancing a little more complicated than if it was on one main loop.

The trick with balancing is to get the rads all heating up at the same time and getting to peak temps at the same point, it reduces extended running times and maximises efficiency

What stat is it?

 

[desktop987456]

I don't mind that at all. Thanks for clarifying, after all I was led by your guidance to get this far! It is Drayton wired Room Stat.

The 3/4" tees off at certainly points and heads in several different directions to feed rads in different 'zones'

Correct. Surprisingly, the balancing was very smooth and I got nice even temperature at all rads @ C2 setting.

With external pump, should it be running all the time or do I need to wire it with Switch Live in boiler? Whats the best practice in industry.
Secondly, how do I get the boiler out of Serv mode, it is only running in that mode so far that I have tested it for balancing.

 

[fixitflav]

With external pump, should it be running all the time or do I need to wire it with Switch Live in boiler?

It shouldn't be running all the time. Some boilers incorporate pump overrun, where the pump is powered from the boiler and runs on for a few minutes after the stat is satisfied and firing stops. Otherwise the pump and boiler are wired in parallel and both start/stop at the same time. I think yours is the latter, but whoever wired it up should have known.

Secondly, how do I get the boiler out of Serv mode, it is only running in that mode so far that I have tested it for balancing.

I've looked fairly briefly at the service manual online and can't see any reference to Serv mode. Can you point to it or give more details?

 

[desktop987456]

pump and boiler are wired in parallel and both start/stop at the same time

Yes.

I've looked fairly briefly at the service manual online and can't see any reference to Serv mode

When the thermostat calls for heat; fan on boiler starts and after a brief period shutdown. The screen shows the water temperature starts from 100deg C and quickly goes down to 30s. It stays there forever.
I then have to reset the boiler by turning the CH knob to reset and then counter clockwise which goes into 'Serv' mode and boiler fires up in that mode until I have to shut it down manually.

 

[Madrab]

Correct. Surprisingly, the balancing was very smooth and I got nice even temperature at all rads @ C2 setting.

With the new pump and new system then that will help with the system balancing and with 1/2" feeds to the rads then they all receive the same flow and pressure, so all's good, just keep it that way, well dosed with inhibiter etc.

That boiler will happily feed the pump and control it's overrun and comes with a pump supply cable that connects to the board,0000 so the boiler will feed the pump directly incl overrun which is what you want

 

[Madrab]

Remove the stat and set the boiler cabling back to the way it was and run the boiler directly and see if that changes things, how/where are you connecting the stat? What kind of stat is it? If the boiler is reaching 100Deg then it's overheating so something isn't firing the pump up, how is the pump connected at the moment?

 

[fixitflav]

That boiler will happily feed the pump and control it's overrun and comes with a pump supply cable that connects to the board,0000 so the boiler will feed the pump directly incl overrun which is what you want
View attachment 318509

The manual I found showed this, pump isn't shown as clearly, but I missed it.

desktop987456 said

pump and boiler are wired in parallel and both start/stop at the same time

Yes.

so it seems the pump has been connected separately, but it should still work OK. From the symptoms, I wonder if the pump is running at all. desktop?

 

[Madrab]

The manual I found showed this, pump isn't shown as clearly, but I missed it

The boiler is a 41-819-21, so the manual for it is here - 101-w Compact and is where I took the snapshot of the pump wiring diagram from.

 

[desktop987456]

Remove the stat and set the boiler cabling back to the way it was and run the boiler directly

I have tried bypassing the Room Stat and tried to connect boiler directly with same result. It doesn't fire up. It only fires up when I reset it and it goes in 'serv' mode.

The boiler and pump are connected to the wiring center. Wiring center N,L and E is fed by Spur. The Programmer and Room stat are installed away from boiler (inside lounge) and it gets its N and L from home wiring in lounge. There is no separate wire for Switch Live or pump Live to boiler. The wiring center has only N,L,E connections for Boiler and Pump. I suspect the wiring is not correct.

 

[desktop987456]

it seems the pump has been connected separately

Yes, Pump is connected to the wiring center, when there is call for heat, I can hear the pump circulating water when boiler fan starts its purge cycle.

 

[desktop987456]

What kind of stat is it

Its a wired Drayton Room stat (old dial type).
This is how I get into Serv mode.

 

[desktop987456]

As per attached trouble shooting steps; the fan starts as soon as boiler is switched on but then it doesn't get to ignition stage and I don't see any error message on display, it just shows water temperature on screen.

 

[fixitflav]

The boiler is a 41-819-21, so the manual for it is here - 101-w Compact and is where I took the snapshot of the pump wiring diagram from.

OK thanks. Thinking about it again, my idea that the pump isn't running is a non-starter as he's got the rads hot and balanced.

 

[fixitflav]

As per attached trouble shooting steps; the fan starts as soon as boiler is switched on but then it doesn't get to ignition stage and I don't see any error message on display, it just shows water temperature on screen.

As you have to stop it manually in Serv mode it must be getting a Fire signal independent of the roomstat. The puzzle is why it won't fire in normal mode. It's difficult to analyse remotely! It might be worth rechecking the wiring and ensure it's in line with the manual.
Any chance that Viessmann could throw any light on it?

 

[desktop987456]

Wiring a Viessmann

I'm swapping a Potterton for a heat only Viessmann. The Potterton has a switched live, and pump live. Does anyone know if I can use the 1 and L terminal on the Viessmann as the switched live, and pump live? Or is the only way to have pump over run, is to use the flying lead supplied with the...

www.diynot.com

See post 4 on this link.