The Efficient Home Forum

OptiMiser wrote:Our S-plan plus system has worked well for a few years with a BDR91 relay controlling the 2-port valve to the radiator circuit, while other "traditional" controllers manage the UFH and DHW valves. When there is no call for heat from Evohome the CH 2-port is closed, so no water can circulate through the radiators if UFH fires the boiler.

I'm thinking of rejigging things to add Evohome control of the DHW and single-zone UFH via a new relay each. AIUI when either of these needs heat Evohome will trigger the relevant BDR (to create a flow path), plus the one that it thinks is connected to the boiler (to generate and pump heat). It also assumes that there is no CH valve, and that the path to radiators is open all the time (hence "standard" design of latching the CH 2-port open). So presumably it ensures the HR92 are fully closed if choosing not to supply heat to those zones.

I realise it isn't the "official" wiring approach, but I'm missing why it would be wrong (as in unintended effects) to take a BDR to each zone valve. When UFH or DHW needs heat Evohome will effectively trigger the boiler twice (via relevant zone valve plus the CH valve which it thinks is "appliance control"). But as long as the HR92s are closed then nothing unexpected will happen.

I prefer to keep electrical control of the CH valve as I think it is better for the valve mechanics: less constant strain on the spring and less likely to sieze open.

So does Evohome ensure the HR92 are closed? Am I missing something else?

OptiMiser wrote:

The EVOHOME Shop wrote:

OptiMiser wrote:It's the first time I've seen that risk mentioned.

Who else with 8 years of evohome experience that you have asked before?

Operating a zone valve 6 times an hour, will cause excess wear and tear on the synchron motor and mechanism. At the end of the day, evohome wasn't designed to operate like your option C, so why would you want to?

I'm not sure if the first bit is rhetorical. I haven't considered it / asked since installing installing Evohome almost exactly 6 years ago, so everyone would have had 6 years less experience then. ISTR the general advice was to try and follow the Honeywell designs, but no-one mentioned potential valve problems.

Most of the reading about V4043 valves I've done over the last 25 years or so has suggested that being energised for long periods in hot areas is the main cause of failure. That fits with the only time I've had one fail about 15 years after install on the CH circuit in a DHW airing cupboard. Hence my query about whether load compensation leading to long hold-open times might be the risk. The one we're discussing runs in a much more friendly temperature location.

So that's where I was starting from, and I appreciate the advice that the extra switching cycles of Evohome have been know to cause problems.

As to why do it the wrong way now: I think we're agreeing there is no detriment to the way that Evohome works. For now it's simpler to leave that part of the wiring as is, accepting that if the zone valve does fail I'll then have to do the same work that I could do now. I so also still prefer to be exercising the valve rather than leaving it latched open - but can't find any V4043 tech sheet to say how many cycles the valve is designed for to help me figure out if this is sensible or not. Finally, the option of popping a traditional programmer back in place if a selected emergency heating engineer is unfamiliar with Evohome or to take ~£1000 of Evohome kit with me if I move house is attractive.

Clareman wrote:In my previous house I used smart radiator valves, not Evohome, while keeping the zone valves. It worked fine, for many years.
I agree with you that exercising the valves is better than risking it jamming. I had one jam on me, due to lack of use over the summer, and it was a right PITA having to replace it.

The EVOHOME Shop wrote:The first bit was a small joke reference to the fact you said it was the first time you had ever seen the risk of TPI'ing a motorised zone valve. Think nothing of it.

The 'issue' with having a zone valve for heating between the boiler and the HR91/HR92 is that evohome doesn't know it is there. So if it does fail, the evohome system doesn't work. There is no need for it to be there. Electrically disconnect it and latch it open.

kartingmad wrote:

The EVOHOME Shop wrote:The first bit was a small joke reference to the fact you said it was the first time you had ever seen the risk of TPI'ing a motorised zone valve. Think nothing of it.

The 'issue' with having a zone valve for heating between the boiler and the HR91/HR92 is that evohome doesn't know it is there. So if it does fail, the evohome system doesn't work. There is no need for it to be there. Electrically disconnect it and latch it open.

I contacted your salesteam to clarify whether the solution for a single radiator using a remote sensor was to use an existing motorised valve (already in place) and to have the motorised valve controlled by the BDR and was advised (in writing) that that was the correct application - I then bought the kit (based on that suggestion).

So are you saying that I should have the remote kit wall kit (which included a bdr) signal to a HR91, if so why do I need the BDR.

The reason for not going for a straight HR91 solution and latching the valve was because the radiator / HR91 are obscured and would not be sensing the room temperature