OV to sealed system

[desktop987456]

Thank you Mottie and Rob for your help.

 

[desktop987456]

Update :
I have installed a dedicated boiler Viessmann 100-w heat only boiler with external pump and an EV on boiler's flow. The intent was to connect it to a vented hot water cylinder.
I have filled system with pressure guage showing 1.5 bar on boiler piping, the boiler turns on but it keeps showing the temperature on display. It doesn't go through the ignition sequence even in 'SERV' mode. I have checked with viessmann and the boiler can be used for open or sealed system.
Could it be a circulation issue because these boilers work on the principle of 'no flow no go'. Any ideas or suggestions please.

Thank you.

 

[Madrab]

All valves open? Invariably the first thing to start in the sequence is the pump, not sure if that particular boiler has a proving switch that then allows the rest of the sequence to activate.

 

[desktop987456]

All valves open? Invariably the first thing to start in the sequence is the pump, not sure if that particular boiler has a proving switch that then allows the rest of the sequence to activate.

All valves open. The boiler has a flow switch, I'll check if it works.

 

[desktop987456]

I am facing the same issue. Before I install the boiler, I opened the flow switch to service it but couldn't get it out completely so turn the sealing nut back on.

After installing the boiler I am facing the exact symptoms. Any ideas., Can't get flow switch locally.

 

[dilalio]

Deleted. Asked a question already answered!

 

[Madrab]

Not sure if that switch can be tested/shorted out

Can you feel the pump running at initial start up, is it actually turning? If so then it can really only be another couple of things as indicated by the fault finder. As far as getting the flow switch out then difficult to say without seeing it, never had to replace one on that boiler before. That being said it, it looks like it's just a knurled plastic nut that undoes and then the switch should just pull up and out, probably just tight in there. Not cheap to replace though.



Apart from that then time to start ruling out things then I guess. If it came to it, I'd bypass the system and run the flow directly to return and see if it starts. That'll rule out the boiler as the issue.

 

[dilalio]

Transit bungs left in?

 

[desktop987456]

Not sure if that switch can be tested/shorted out

Can you feel the pump running at initial start up, is it actually turning?

I managed to get the flow switch out.

After putting it back into boiler, when i start it in 'SERV' mode, the boiler did fire (previously it wasn't firing).

My queries are now:
It is only firing in 'SERV' mode - How do I get it work in normal mode for DHW only.
- The thermostat for indirect to act as call for heat to the boiler, where would it go considering that boiler needs to start heating the water if water temperature goes below the setpoint e.g. 40degC? This would mean thermostat from indirect goes to port 96 on the boiler's PCB? That is how thermostat is connected for my separate boiler for CH system. (exact boiler 100-w OV)
- The temperature sensor from indirect goes to sensor 5 (two red jacks sticking underneath the boiler). I am confused as what are these sensors telling the boiler, if I have thermostat in the above point?

Thanks

 

[desktop987456]

Transit bungs left in?

Could it be? I have checked the circulation without the boiler for piping from pump to indirect's flow and return and it works fine.
How could I check for blockage in boiler's HEX? It works in 'SERV' mode now.

 

[desktop987456]

Message from Viessmann
Good Afternoon
It is not recommended to use the probe sensor on your boiler model as it is a heat only and does not have temperature setting for the DHW, your Cylinder will most likely have its own thermostat to set the temperature at, this then provides a 240 v switch to call for heat from the Boiler ( subject to the makeup of the heating system and zone valve operation), this switch live can be taken to a Cylinder Demand Box, 7574319, which would put a heat demand on the boiler until the thermostat is satisfied.

Kind regards

I wrote:
Thank you, I am intending to dedicate the boiler to serve the dhw cylinder for it's heat demand at one temperature setting, should it work with the sensor? The boiler has sensor 5 probes coming out from x20 socket.

Message from Viessmann
Good Morning
The boiler requires a switch signal to turn On / Off, it is not possible to use the Sensor as
1. It has no DHW set point to configure and
2. The Boiler would not receive an On / Off to satisfy the demand so could potentially run constantly

As explained before, you could use the Cylinder Demand box which would just ramp the boiler straight up to High Fire, this woulod switch on / off from the Cylinder Thermostat, or you can just bring the switch live demand back to plug 96 of the boiler.

Kind regards

 

[fixitflav]

I wrote:
Thank you, I am intending to dedicate the boiler to serve the dhw cylinder

You said in #13 it's for CH only

 

[desktop987456]

Apologies, may have mixed them up.
It is for DHW; dedicated boiler.

 

[Madrab]

You need to have a thermostat on the cylinder to control the cylinder HW temps, no other option is acceptable to ensure proper control. That is then just wired in through the SL to the boiler so the stat is in control of the HW

I believe the Viesmann's cylinder demand box is their way to implement PDHW but if you are only using the boiler for the cylinder then you can just set the boiler to fire @ MAX and then the cylinder stat will shut the boiler down once the HW temp has reached set point.

 

[desktop987456]

You need to have a thermostat on the cylinder to control the cylinder HW temps, no other option is acceptable to ensure proper control. That is then just wired in through the SL to the boiler so the stat is in control of the HW

I have installed a bi-metallic thermostat on cylinder and wired it on port 96 of the PCB.
HW thermostat - 70
Boiler thermostat - 65-70
pump speed - C2 (flomasta 5m head pump)

The issue is that in the morning when I start the boiler (timer) it fires at full blast but then it starts to modulate after reaching 50DegC and once it reaches its set point 70DegC, burner gets off. It then restarts after return temp falls below 50DegC, the modulating burner startes with just 20% and stays lit for a couple of minutes before temperature reaches set point again (65DegC-70DegC).

It seems that boiler is cycling, how do I keep the burner on for longer so it heats up the cylinder to 55DegC?

Thanks in advance