boiler pressure question

treko

Viessmann Vitodens 100W boiler

2 - zone heating

2 -grundfos 15-58 pumps

1- 3 way manual mixing vavle

Hooneywell R8239D controller



Originally the boiler was running one zone with the controls hooked up to the boiler PPM. The solenoid valve was placed in the open manual position.

Recently a second zone was added. The primary pump is controlled by the boiler and the second pump feeds both zones.

When the zones are satisfied and the SV close the primary pump continues to run for the default set time, however the boiler pressure increases from approx 20lbs toas high as 30lbs. It has also activated the PRV. I assume this is abnormal, and not having much experience with boilers, any thoughts as to why this increase in pressure.

Thanks

Zman

Abnormal

Yes, very strange. Do you have a drawing or picture? Where is the expansion tank in relationship to all this?

Carl

treko

Zman

Thanks for the reply.

I attached a basic drawing of the circuit. Its a simple system. Should the pressure, as long as the primary is running, remain a constant value? It is staying under 30lbs lately, however it still fluxuates.





Thanks

Zman

Questions

Is the expansion tank piped in front of the circ and the spirovent behind?

Are there any check valves?

Carl

treko

Re: Questions

The tank is basically piped between the primary boiler pump and the zones pump. The spirovent is in front of the secondary zone pump. There is no check valves in the system. Another way is, the returns from the zones come together, then thru the spirovent, then the sec. pump, then the exspansion tank, then to the boiler. Hope that makes sense.



 I apoligize for not having the correct terminology. 

Thanks for the reply.

Zman

Fill valve

Is the fill valve attached to the spirovent?

Carl

treko

Zman

The spirovent has a 1/2 pipe from the bottom to a Watts1156F( not sure what the device is called ) with a range of 14-17 PSI, then to backflow preventer, then to domestic water suppy. You asked earlier about a check valve, my mistake, there is one at that point.



Thanks

Zman

3way

I think you problem lies in the location of the expansion tank and fill valve. The expansion tank, located in front the circulator is causing the pressure to drop at the fill valve. Every time the circ comes on, the fill valve adds a bit of water to the system. The tank should be on the other side.

What has me puzzled is the purpose of the 3 way valve.

I don't understand the boiler piping intent.

Carl

treko

3way

the valve for filler water has been closed for a while.

3 way-The installer recommended it, however i cannot recall the reasoning except for to prevent cold water shocking the boiler. Would a tee have been sufficient?

Thanks for you insight.

Zman

Re pipe

I think you should pipe the boiler according to the manual. There is no need for a mixing valve to prevent shock. Someone would have to evaluate the flow requirements to decide if it needs to be primary/secondary.

The issue you are having is related to the odd piping.

Carl