Turned my heat-only boiler into a combi!

[echoes]

Hi,

I spent yesterday on a project inspired by a noisy shower pump and a high-pressure-shower loving wife.

Basically I've ditched the pump and fed the shower mixer at mains pressure by adding a (modified) 3-port valve, plate heat exchanger and flow switch.

I have a WB 24 RI boiler (sealed system) pictured here:

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• echoes
• 11 Nov 2011
• 1

In the next picture you can see the plate heat exchanger, diverter and flow switch:

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• echoes
• 11 Nov 2011
• 1

And here's the existing motorised valve and bypass (S-plan):

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• echoes
• 11 Nov 2011
• 1

The diverter valve is a standard Honeywell mid-position valve which I had spare, but I modified it to make it into a diverter valve. This involved breaking a couple of tracks on the circuit board, and soldering in a new link:

1) Break white from SW1 NC
2) break D1 from SW2 NC
3) link SW1 Com to SW1 NO

This winds the valve to position A when Grey is energised. When the valve is fully wound, SW2 closes, so I now connect White to permanent live and Orange to switched-live to fire the boiler as you would with an S-plan.

The shower works really well - significantly higher pressure and flow than the pump (which was a Salamander 1.7 bar) and much quieter of course. Also won't run out of hot water by having long showers!)

The existing cylinder still provides hot water to the bath, basin and kitchen.

I will lag the rest of the pipework before it gets frosty!

 

[toasty]

Nice! Those German heat exchangers off eBay are really good - I've used a few to fit new boilers to old systems.
That's a really nice job you've done.

 

[echoes]

Thanks toasty! I was really pleased with the eBay German HEX - only £40 and delivered with stereotypical German efficiency!

I do think I need to restrict the flow slightly though: when the mixer is fully open and the shower head on it's fastest flow, the boiler can't quite keep up. I'll try turning the isolating valve off slightly.
[Or a couple of pennies with holes drilled through the centre inserted in the mixer valve connections would do the trick.]

 

[htgeng]

probably worth putting up a complete wiring diagram for the benefit of someone looking at this in a years time. Your flow switch is connected to your grey? Personally, I'd have used full bore isolators to your phe rather than gates.

You can buy 15mm flow restrictors for about £4. look on bes.ltd

 

[echoes]

Thanks for the input hteng - much appreciated

Point well taken about the gates, but I may wait until the next drain-down opportunity before replacing those... unless I feel brave and snatch them one at a time....

Do you think it would make that much difference to to the flow through the HEX?

Already have an order saved at BES for the flow restrictor valve & cartridge - just waiting to bump it over £40 for free delivery... glad I was thinking along the right lines.

Yes flow switch on the grey cable.
Wiring diagram also a good idea, as well as a sticker on the 3-port warning that it's been doctored.

 

[toasty]

Next job should be to obtain a thermostatic mixer valve and another pump and then run the whole hot water system from this....

Why?

Because then you could repurpose the hot water cylinder as a thermal store, meaning that you should be able to sustain a full bore shower, as well as benefiting from less boiler cycling with central heating.

 

[echoes]

I do have a spare pump and have had thoughts about repurposing the cylinder as a thermal store. But it's a project for another year.
I've been reading the sagas on thermal stores/heat banks on the plumbing forum and think that done properly they could be very good.

However I do think at the moment it's a lot of faff for not much benefit - diminishing returns and all that. And there's the added benefit of no moving parts / nothing-to-go-wrong with a standard vented set up... I'll keep you posted though!

 

[echoes]

Now fitted an isolating/restrictor valve with an 8 L/min restrictor in the hot feed to the shower. Works a treat!

 

[toasty]

Nice,
Gonna go for a similar system in my next house.
No cylinder, just a nice sized boiler (in fact probably two small ones) and a dirty great big heat store and localised heat exchangers for each bathroom. Obviously with well lagged flow and returns.

It's the best way,
Dan