Help and advice please - upgrade to independant h/w and c/h

[fergusondj]

I'm looking for advice on the best way to upgrade my central heating system. We live in a two story house with the boiler, pump and controls downstairs and the h/w cylinder upstairs.

The current system is open vented but without an independent hot water circuit (or cylinder stat for that matter). There is a tee from the boiler flow, one branch goes directly to the cylinder, the other to the C/H via a zone valve, therefore I can have hot water only but when the central heating calls for heat the flow from the boiler still circulates through the cylinder. Ideally I'd like a fully independent setup to save some money and stop the h/w getting too hot.

So, first thoughts are simply put another valve on the cylinder circuit but, and here's the problem, the feed and expansion is connected via a tee just before the pipe goes into the cylinder. I can't fit a valve before this tee as I'd turn my system into a sealed one with predictable results!

Can I put a valve on the cylinder return circuit without encountering any problems? - I'm worried about overrun or drawing in air from the feed and expansion pipes.

I appreciate the current system is far from ideal as the feed and expansion should have been fitted before the pump - I expect it was plumbed the way it was originally to save time and effort - this was easily 30+ years ago and the pipework is far from accessible now.

Any and all help/advice gratefully accepted

 

[Agile]

You dont say what model of boiler you have or if it has a pump over run.

It really does need some experience to examine a system to make it fully pumped without problems if its open vented.

There is no point in me making any suggestions when I dont know how your system is configured.

Tony

 

[fergusondj]

It's a Baxi Main boiler, I have no idea if it has an overrun to be honest.

 

[Agile]

Main is the make. Only the model will determine if it has over run.

At this point my advice would be to get a professional to examine the system and specify how to achieve the full controls.

Tony

 

[D_Hailsham]

It sounds like a semi- gravity system which has possibly been partly converted to fully pumped.

There is an arrow on the body of the pump. Which direction does it point - towards the boiler or away?

How many water pipes connect to the boiler?

 

[fergusondj]

Two pipes connect to the boiler - I can't confirm 100% on the question of pump flow as the boiler is at one end of the kitchen (mounted high on the wall in the utlity room) and the pump and valves are at the other (behind a panel at the back of some base units in the kitchen proper) the pipes to and from the boiler are above a dropped ceiling and then drop to floor level. - I'm pretty sure the pump is on the flow though.

 

[fergusondj]

I checked with heateam and it doesn't need an overrun as it has aluminium heat exchangers.
.
I suppose I could fit a valve onto the cylinder return and see if all is OK. Apart from pumping over into or drawing in air from the feed and expansion tank should I worry about anything else doing this?

 

[D_Hailsham]

I suppose I could fit a valve onto the cylinder return and see if all is OK. Apart from pumping over into or drawing in air from the feed and expansion tank should I worry about anything else doing this?

Earlier you said:

There is a tee from the boiler flow, one branch goes directly to the cylinder, the other to the C/H via a zone valve.

Where is the pump? Before the Tee or after?

Putting the valve in the return is standard for the Honeywell C plan. Although this is a semi-gravity system, the fact that your boiler does not have pump overrun means there is no possibility of water being forced out of the vent pipe because the HW valve is closed.

An automatic bypass would be a good idea.

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[fergusondj]

Thanks for your reply, the pump is before the tee.

I was worried about pumping over into the expansion tank when the h/w circuit is closed by the new valve and the central heating is circulating - am I worrying unduly then?

Re your point about an automatic bypass my system has TRVs on all rads exepct the bathroom - is that sufficient?

 

[D_Hailsham]

I was worried about pumping over into the expansion tank when the h/w circuit is closed by the new valve and the central heating is circulating - am I worrying unduly then?

Re your point about an automatic bypass, my system has TRVs on all rads except the bathroom - is that sufficient?

Not really. As the TRVs close down the flow rate through the pump reduces and the pump pressure increases. The same thing happens when one of the valves closes. This could mean that the flow rate through the boiler drops too low. The bathroom rad will help when the CH is on, but will have no effect if only the HW is on. An ABV, fitted immediately after the pump connecting flow to return, will overcome all these problems.

Will your timer/programmer allow separate times for HW and CH? If it doesn't, you will have to change it. If you don't know, just post the make and model no.

 

[fergusondj]

My programmer does have separate times for h/w and c/h.

 

[D_Hailsham]

My programmer does have separate times for h/w and c/h.

Then you can insert a motorized valve in the HW return and wire as an S Plan

Don't forget to put an ABV after the pump.

View media item 72

 

[Agile]

I would be very surprised if you dont need pumpover run when fitted to a fully pumped system.

You only need an ABV if it does have pump over run.

Normally the boiler would have the facility to drive the pump to provide over run even if the boiler does not need it when connected to a gravity hot water circuit.

Tony

 

[D_Hailsham]

I would be very surprised if you dont need pumpover run when fitted to a fully pumped system.

I checked with heateam and it doesn't need an overrun as it has aluminium heat exchangers.

Current Main System and OV boilers have overrun.

OP: What is the model number of your boiler? The GC Number would also help.

You only need an ABV if it does have pump over run.

The purpose of an ABV is not just to provide a path when the valves are closed.

Main OV: "The system must be designed to always provide a route for water to circulate between the boiler flow and return. Best Practice is to use an automatic bypass."

Main System: "The boiler is fitted with an automatic integral bypass."

 

[Agile]

An ABV does not provide a path unless there is a pump fitted.

A passive path would normally be a gravity cylinder heating coil.

Tony