Hi @editor, has the valve failed or the motorised actuator?

@allyfish the valve is working, and when called upon, opens and/or closes. Apparently there's a microswitch inside these valves, and that's what's not promoting the boiler to come as a redundancy in our system. It usually takes care of defrosts and some heating when we drop below 0C.

Posted by: @editor

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and that's what's not promoting the boiler to come as a redundancy in our system

Thanks @Mars. A 'boiler' you say, this is blasphemy! 

@allyfish 🤣

Unfortunately, it’s the nature of the system we have to work with. The index circuit consistently struggles to reach target temperatures when the outdoor temperature drops to 0°C or below.

In this setup, the boiler only runs intermittently – primarily to assist with defrost cycles or provide a temperature boost when needed. While it’s far from ideal, it’s how the system is configured to operate. One of the reasons why RHH was born. An expensive system to install that has been butchered. 

@editor I see. I knew there would be sound reasons. My ASHP is barely big enough, and I've seen aveage room temperatures drop a couple of degrees overnight with the ASHP running when outdoor air temperatures drop below freezing. Basically, below a certain ambient temperature without supplementary heating, my ASHP seems to track ambient outdoor temperature. There are several factors causing this I think:

1. Undersized unit delivering maximum heat output. When it's defrosting however, it's not delivering 10kWh, more like 8kWh due to intermittency of operation and heat lost for defrost cycle.

2. Return temperature of radiators typically about 5degC lower than supply, which at primary flow rate of 22l/min means the ASHP is, more or less, maxed out: 5x(22/60)x4.2= 7.7kW. It can't reach target WC temperature because it can only raise the circulating water by around 5.5degK.

So it could really use some supplementary heat input 3-4kW. I can energise the 3kW immersion in the LLH, which raises the LWT by a couple of degrees, but that's a very expensive option, even with load shifting most imported electricity off-peak to low tariff. I have the setting for this set to -5degC, by which time I know the house won't be warm enough to be comfortable and will never warm up with around 8kWh of heat input. I  could raise this to 0degC, but then I'm guzzling around 6kWh of energy with ASHP & supplementary 3kW direct electric heating together. So I light the stove and burn some wood, which can quickly boost downstairs, and it filters upstairs. 

I have a bit of the same issue:

However, this is DIY so I can only kick myself. The TWV is crewed on press fittings on three sides with no possibility to losen just one. So if there ever will be an issue, it will be a pretty big operation to get it all sorted. 

@editor - what surprised me most about your picture, is that your piping is completely uninsulated. Although the forum community did actually nominate you for the Nobel Prize for sustainability, this ruined your chances forever 😆. 

For reference, here's the classic motorised valve wiring diagram:

If the valve body itself is still operating, then you just need to exchange the head.

The white wire is only provided on valves which have ports to accept 28mm diameter pipe (or larger).
The common 22mm valves (Honeywell V4043 etc) have a 'single throw' switch.

In the case posted here by @editor it's possible that the Auxiliary Switch has stopped working because debris has fallen in through the slot from which the manual lever protrudes.
He might be able to recover the valve's operation by cleaning it out with a vacuum nozzle.

It's odd that Mars' valve malfunctioned on a Thursday evening.
They normally wait until Friday, when the stores have just closed.

Keep a spare on the shelf!!

Posted by: @transparent

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He might be able to recover the valve's operation by cleaning it out with a vacuum nozzle.

The 2000W Karcher will be out shortly!