Wiring for dual circuit and pump overun?

[AndyTh]

Hi all. First post - be gentle.

I have added major extension to existing house. There are two pumps each supplying a separate CH and HW zone valves. The boiler is a Worchester CDi conventional. The boiler has an overun circuit that keeps the pumps runing for 3 min after the Heating demand stops.

My problem is that when the programmer or stat stops, all the valves close while the pump keeps running for 3 mins. Pump is deadheading and there is no flow through boiler.
How should the pump be wired?

Note that there are two in fact two pumps, how would I control these separately, both for normal operation and during boiler overrun.

Appreciate any help. Cheers
Tried to insert Picture of circuit here, but rejected. How can I share a picture?

 

[AndyTh]

Found insert image but this is all I get.
I am on ipad and trying to load from photos. What am I doing wrong?
[MENTION] [/MENTION]

 

[kozak1968]

You need an automatic bypass valve to be fitted after the pump and before the 2 port valve. This will allow a flow through the boiler when the call for heat is off which will protect the heat exchanger.

 

[AndyTh]

maybe picture worked now?

 

[kozak1968]

Do you have a pipework drawing. It sounds like its more to do with the pipework configuration than wiring.

 

[AndyTh]

I see I have managed to post picture twice, but upside down. This should show that I have in total 4 single valves and two pumps.

Kosak - thanks for reply. Not sure how that would work and it brings up another problem. See my other post on expansion pipe and pump over. Is there not an electrical way to solve the problem?

 

[GasmanxxxR1]

You will need an auto bypass, the pipework should never have been put in without one

 

[jtsplumbing]

Why 2 pumps ??

 

[ShaunCorbs]

Why 2 pumps ??

one for heating and one for hot water (heating system must be big)

or a back up for the first one

 

[jtsplumbing]

Would be useful if he told us what size system he is running !

 

[ShaunCorbs]

Would be useful if he told us what size system he is running !

it would or maybe a drawing

 

[AndyTh]

Sorry guys - should have made a diagram - see below. I know the system is not as per modern practice, but the original house system was done as below the dotted line. The new extension is a parallel system above the dotted line (installed by builders and plumber). We will mostly live in the new extension unless the kids are at home in which case the original system needs to operate also.

There are three problems
1. pump over via the expansion pipe,
2. I suspect that the boiler keeps both pumps running, even if the demand is only for one extension
3. all the valves close while the boiler is in overrun and the pumps deadhead.

What solution do you recommend.
1. I could install relief valve and go unvented - I was trying to avoid that.
2. I could just install a pressure relief valve on the expansion pipe.
3. I could install and auto bypass - one for each circuit
4. I could try to managewith one pump - but it is a big system for one pump

 

[ShaunCorbs]

The problem is how it's designed it will always pump over and there should never be a valve in the vent

 

[jtsplumbing]

Already got 16 radiators & 2 cylinders and want to add extra's in an extension ? What size boiler do you have ? Some of the pipe work size is going to need increasing, Don't base it on (We don't use all of system) there will come a time when you will need to, always base it on worse case , to late when everything is finished, Proberly got to much restriction on system and water is taking easy route,

 

[AndyTh]

The diagram shows the complete system with the extension added. It is a 30 Kw boiler, we also have 3 wood burners and electric underfloor. The insulation in the whole house has been upgraded. This should be enough wattage for what is essentially a bungalow with attic bedroms.

I realise that the design is not modern, but many old systems have the pump on the return leg and they have worked for years. I realise that one fundamental problem is that the pump generates more head that the 9ft elevation of the header tank especially when TRVs close - then the expansion pipe is the easy route. Just asking if a relief valve in the vent will be acceptable. I cannot see how that is less safe than a closed system with a relief valve.

However the pump over is a separate problem from how to get flow during the boiler overrun. I thought there might be an extra terminal from the boiler to keep one/any valve open for 3 mins.

If I use an autobypass where should this be installed. If it is directly between the flow and return, then the pump will only circulate a limited volume of water with little cooling of the heat exchanger. I could bypass around the motorised valve for the HW, then at least there is a larger volume circulated with cooling. I am also not sure how to adjust the bypass pressure.

Just looking for advice guys.

 

[ShaunCorbs]

tbh there so much wrong with your design/ existing system, you have two options either re do (which would be easier) or many many repairs

read this and you might get a better understanding where were all coming from

http://bpec.org.uk/downloads/CE30 - Domestic heating by gas.pdf

 

[jtsplumbing]

If you read the installation book for the boiler it show's diagrams of there recommended way of installing the system, who's idea was it to add another pump ? Just arrange pipe work & controls as manufacture advise,

 

[stevetheplumber]

one pump motorised valve for each zone and move cold feed and vent or seal the system and add a bypass

 

[thompsonbrown]

As above needs an auto by-pass installed after pumps.

 

[Sparkgap]

Sorry guys - should have made a diagram - see below. I know the system is not as per modern practice, but the original house system was done as below the dotted line. The new extension is a parallel system above the dotted line (installed by builders and plumber). We will mostly live in the new extension unless the kids are at home in which case the original system needs to operate also.

There are three problems
1. pump over via the expansion pipe,
2. I suspect that the boiler keeps both pumps running, even if the demand is only for one extension
3. all the valves close while the boiler is in overrun and the pumps deadhead.

What solution do you recommend.
1. I could install relief valve and go unvented - I was trying to avoid that.
2. I could just install a pressure relief valve on the expansion pipe.
3. I could install and auto bypass - one for each circuit
4. I could try to managewith one pump - but it is a big system for one pump
View attachment 24411

SOOOO much wrong!!!
1) Repipe cold feed into boiler return.
2) Fit auto bypass valves to pump circuits
3) Change pump positions to put pumps on flow so systems are under positive pressure (you'd be surprised how many systems I've come across where they've fitted rads in a roof and wonder why they keep getting full of air!)
4) Rehash flows to cylinders so you just have the open vent off the boiler to stop pumpover.

Used to come across open vents on old gravity systems in schools where they'd fitted an air vent and safety valve over the f&e tank to stop pumping over once they put in pumps.