Evohome Hot Water Safety

[thepook]

how close did you mount the BDR91 to each other?

for your existing boiler i would go for 6 cycles and 2 minutes minimum run (standard being 1)

in my opinion the so called 's-plan minus' is the optimal system (and what I have at home)

They are about 1.2m apart, as I fitted the heating where the old roomstat was, the dhw where the old programmer was and the added the boiler demand by the boiler, but a little over 40cm away. They are all a min of 30cm from the boiler, pipework or other metal objects.

As I said, I have now removed the boiler demand bdr91again, as it didn't seem to play nicely with the heating zone valve bdr91. Unfortunately that means that I can't set cycle rates again until I convert to s-plan minus when the new boiler goes in.

The s-plan minus does seem to be the best way to have full control with the minimum of components - as an engineer I firmly believe in the simple is best approach where possible.

[The EVOHOME Shop]

They are about 1.2m apart, as I fitted the heating where the old roomstat was, the dhw where the old programmer was and the added the boiler demand by the boiler, but a little over 40cm away. They are all a min of 30cm from the boiler, pipework or other metal objects.

As I said, I have now removed the boiler demand bdr91again, as it didn't seem to play nicely with the heating zone valve bdr91. Unfortunately that means that I can't set cycle rates again until I convert to s-plan minus when the new boiler goes in.

The s-plan minus does seem to be the best way to have full control with the minimum of components - as an engineer I firmly believe in the simple is best approach where possible.

I have had an idea! What about a Y-Plan minus?

If you look at the wiring diagram on page 47 of the evohome installation manual.

If you wire the system firstly moving the white wire from the B terminal of the HTG BDR91 to the permanent live terminal 1 on the diagram (so the heating port of the Mid Position Valve is always open), wire the DHW BDR91 so that the B terminal has no wire to anything (remove wire from DHW BDR91 B terminal and terminal 8), but make sure the C terminal is still wired to the grey wire of the Mid Position Valve. Remove the orange wire going from the Mid Position Valve and make it safe in another terminal. Then wire the B terminal of the HTG BDR91 to terminal 8 (boiler/pump switched live) and configure the HTG BDR91 as a 'boiler relay' and the system through stored water guided configuration as 'hot water only'.

This should have the desired effect you are looking for, using only two relay boxes and HR92's on all radiators on the heating side!

[thepook]

I have had an idea! What about a Y-Plan minus?

If you look at the wiring diagram on page 47 of the evohome installation manual.

If you wire the system firstly moving the white wire from the B terminal of the HTG BDR91 to the permanent live terminal 1 on the diagram (so the heating port of the Mid Position Valve is always open), wire the DHW BDR91 so that the B terminal has no wire to anything (remove wire from DHW BDR91 B terminal and terminal 8), but make sure the C terminal is still wired to the grey wire of the Mid Position Valve. Remove the orange wire going from the Mid Position Valve and make it safe in another terminal. Then wire the B terminal of the HTG BDR91 to terminal 8 (boiler/pump switched live) and configure the HTG BDR91 as a 'boiler relay' and the system through stored water guided configuration as 'hot water only'.

This should have the desired effect you are looking for, using only two relay boxes and HR92's on all radiators on the heating side!

I like your thinking Richard - I guess the only question is how long the valve motor would survive powered and hot the whole time?

[thepook]

One further thought, but it would mean draining down....what about turning the valve upside down so the dhw port was sprung closed, then wire the white wire to the b terminal of the dhw bdr91, so that the valve would motor to mid position on dhw demand?

[top brake]

Actually, the reason I am as keen to find out as ever is that I bought an additional (3rd) BDR91 to use as a boiler demand (I think that is the same setup Rameses on here has - y-plan with 3 BDR91s). When I configured this setup, I found that I could set the boiler demand cycle rates, and went for 4 minutes minimum on time and 3 cycles/hour. However, what I then noted was that the Boiler demand responded as I would expect (on for 4 minutes minimum), but the heating zone valve BDR91 was only on for short durations e.g. only 1 minute sometimes (DHW was set to off). This meant that the boiler was firing for 3 minutes out of 4 without the heating zone valve on - surely that can't be right? I know on a y-plan its not a disaster, but on an S-plan (and the controller wouldn't know any different as the 2x2 port and 1x3 port is the same option in the binding) the boiler would be firing and pumping straight through the bypass valve.

Any thoughts?

I have since removed the third BDR91, done a full reset/cleared all binding and reconfigured as a conventional y-plan with the 2 BDR91 bound as 1x3 port valve in guided config, but I am still seeing short firing times from the heating zone BDR91. Have seen less than 1 minute when close to target temperature.

Some initial information I can share on this.

As you have found having a S/Y Plan plus Boiler Relay system will not work.
It was never designed/intended/published to work in this way.

Regarding cycle rates on an S/Y Plan plus HR92 zoned system an explanation is being prepared.
When I have something that can be easily explained and understood in laymans terms I will share it.

[thepook]

Some initial information I can share on this.

As you have found having a S/Y Plan plus Boiler Relay system will not work.
It was never designed/intended/published to work in this way.

Regarding cycle rates on an S/Y Plan plus HR92 zoned system an explanation is being prepared.
When I have something that can be easily explained and understood in laymans terms I will share it.

Very interesting, thanks - I look forward to your further info.

cheers,

thepook

[paulockenden]

Regarding cycle rates on an S/Y Plan plus HR92 zoned system an explanation is being prepared.
When I have something that can be easily explained and understood in laymans terms I will share it.

Did this ever happen Top Brake? I think it probably relates to the short-cycling thread elsewhere.

P.

[top brake]

Did this ever happen Top Brake? I think it probably relates to the short-cycling thread elsewhere.

P.

It was covered on the webchat, essentially the demand is driven from the HR92s there's no minimum run time with S Plan configuration.