pumping over & c plan to s plan

[77up]

New boiler installed (May) -installer didn't check suitability of pipework - apologised - would return to fix it - still waiting. The main features of the pipework - feed and vent pipes are connected to the HW circuit -return and flow respectively - pump on the return side. So, at present - a fully pumped system alongside a C plan pipe framework!
When HW is on the CH is heated as well - no pump over.
When CH is selected - pumping over - WHY ?? - more importantly what solution can anyone give me. Is it because an S plan has not been installed or can there be another reason causing this problem.
I have checked for blockages - none
Cut down the pump speed - no effect
There is no room to heighten the vent pipe
As the CH works perfectively when HW is selected then ,surely, the pipework design is okay.

Can anyone help to determine where to site the zone valve when I get round to installing an S plan layout. According to the plan it should be fitted on the HW flow pipe.
Should it be fitted between the boiler and the vent pipe ,or, between the vent pipe and the hot water cylinder ?? Remembering that my pipework is not as indicated in the S plan schematic.

 

[45yearsagasman]

View media item 32248There ya go.

 

[77up]

I would have ticked thanks earlier but the diagram only appeared this afternoon. I did wonder about the comment ' there ya go ' on its own.
It would a

 

[77up]

I wondered what the consensus of opinion is concerning combining the feed and vent to overcome the problem of pumping over ??

 

[Terrywookfit]

A sketch of your actual system would be handy !!

 

[45yearsagasman]

I posted that on Monday approximately 2.5 hrs after your request for a pipework layout for S plan open system. The phrase "there ya go" is, or be should be self explanatory when giving someone what they asked for.

 

[D_Hailsham]

The main features of the pipework - feed and vent pipes are connected to the HW circuit -return and flow respectively - pump on the return side.

Your old boiler would have had a low resistance heat exchanger so the pressure difference between feed and vent pipes was negligible. Modern boiler heat exchangers have much higher resistance so the pressure difference would be much higher if the feed and vent are on opposite sided of the boiler. The feed and vent will have to be on the same side (usually the flow, as in 45's diagram) to eliminate the pump over. They also need to be connected to the flow pipe within 150mm of each other. Connecting to a horizontal pipe, as in the diagram below, is preferable.

Feed and Vent

• D_Hailsham
• 17 Oct 2010
• 1

 

[77up]

Thanks for all of your comments and suggestions so far - keep up the effort lads - most appreciated. Terry - I'm working to provide a diagram. The pipework at present is similar to a standard set up apart from the differences I stated at the beginning. It's my understanding that the format indicated in my initial post was standard practice in the 80's and possibly into the 90's.

 

[Hugh Jaleak]

Can anyone help to determine where to site the zone valve when I get round to installing an S plan layout. According to the plan it should be fitted on the HW flow pipe.
Should it be fitted between the boiler and the vent pipe ,or, between the vent pipe and the hot water cylinder ?? Remembering that my pipework is not as indicated in the S plan schematic.

Under no circumstances fit any type of valve in the flow between the boiler and the open vent. The boiler requires an open path via pipework in a constant rise from the boiler to over the F&E cistern, interrupting this makes the system potentially dangerous! Pump and valve must be fitted after the vent, as per the 2 diagrams above.

 

[Agile]

When I read this the first thing that I think is the it is the paid boiler installer who should be advising you and working to correct the problem.

Was he a cheap, less than interested installer, generally meaning charging less than about £400 ?

Tony

 

[77up]

Hugh, your warning is duly noted. I appreciate that if the flow pipe is 'obstructed' between the boiler and vent then the vent facility ceases to function as a safety device.

 

[77up]

The long awaited diagram. To reiterate - what do you think is causing a pump over when the system is on C.H. but not when on D.H.W.
What do you think of combining feed and vent pipes as a means to overcome the problem of pump over ?

 

[D_Hailsham]

What do you think is causing a pump over when the system is on C.H. but not when on D.H.W.
What do you think of combining feed and vent pipes as a means to overcome the problem of pump over ?

As you don't show a separate pump, I assume it is in the boiler. This means that the pressure at boiler flow will be much greater than at the return, say 20 to 30kPa - what's left after the heat exchanger has taken its share from the pump.

When valve VA06 is open the coil in the cylinder acts as a short circuit, so the pressure difference between feed and vent pipes is relatively small. But when the valve is closed, the feed and vent pipes are effectively on either side of the boiler. This means that there will be a noticeable pressure difference between the feed and vent pipes, similar to the pressure difference between flow an return at the boiler.

A combined feed and vent is a possibility, but it can only be used if approved by the boiler manufacturer.

What is EX01?

 

[77up]

Sorry about the somewhat misleading diagram. Ex01 was the nearest symbol available to represent the pump - so the pump is not in the boiler. Will that make a difference the pressure differences ?
Ideal does accept combined feed and vent pipes in relation to their boilers.

 

[D_Hailsham]

I assume you have a Logic or Logic+ Heat only boiler. What output?