Remote control of boiler DHW setpoint

conorius · 11 Jul 2006

I have had a Worcester Greenstar 35 CDI installed in the loft space since last april. Everything has been working well since, an I have been generally very pleased.

I have a remote control for the boiler (RF10 optimser ?) located down stairs in the living area. What I would really like to do is be able to adjust the DHW set point remotely ( only two positions required), as my wife likes very hot water for the dishes but only Warm water for bathing our child every evening. This does not seem to be possible.

Does anyone know of a Heath Robinson approach that would remotely turn the Dial ( say wireless door bell with something)

Agile · 11 Jul 2006

Heath Robinson was around rather before radio control and was more used to mechanical contraptions.

He would probably have used a system of rope pulleys.

The control knobs are not designed for regular movement so often.

If I was tasked with that problem I would switch in an additional resistor across the DHW sensor to lower the temp.

Tony

Slugbabydotcom · 11 Jul 2006

By opening the cold tap and reducing the water temperature then testing with an elbow or thermometer before you put the child in the bath is the cheapest way.

OR:

Invest in a thermostatic mixing valve to fit under your bathtaps which will limit the temperature of hot water coming out of the bath tap.

A real Heath Robinson idea of removing re-boxing, extending wires and re-locating the HW potentiometer seems feasible but is not practical and would in my opinion create an ad hoc installation in the eyes of Corgi.

Anything wireless [especially with wireless doorbell parts] is out of the question as every time a trucker goes by and keys up his CB you could end up with a boiled baby. Unless you qualify as a radio ham first just forget about the wireless thing

Gasguru · 11 Jul 2006

A real Heath Robinson idea of removing re-boxing, extending wires and re-locating the HW potentiometer seems feasible

Definately not advisable - the extended wire would act as an efficient aerial for all manner of interference potentially damaging the board along with a dozen other likely problems.

HarrogateGas · 12 Jul 2006

If I was tasked with that problem I would switch in an additional resistor across the DHW sensor to lower the temp.

Modifying a gas appliance.....you could be hung drawn and quatered for that.

breezer · 12 Jul 2006

Agile said:
Heath Robinson was around rather before radio control and was more used to mechanical contraptions.

He would probably have used a system of rope pulleys.

did you know heath robinson, never did anything like that?

apparently he only ever did the drawings, he didn't actually make things (probably because they wouldn't work)

conorius · 12 Jul 2006

Thanks for you suggestion:

"Invest in a thermostatic mixing valve to fit under your bathtaps which will limit the temperature of hot water coming out of the bath tap."

However:
Its seems a pity to waste energy heating the water up a high temperature (with reduced heat transfer efficiency as the water gets to higher temperatures) , only to cool it down with cold water from the thermostatic valve.

Agile · 12 Jul 2006

Thats a common fallacy!

If you take 5 litres of water at 60 C and add 5 litres at 20 C then you get 10 litres at 40 C but no heat is wasted !

Tony

Onetap · 12 Jul 2006

conorius said:
However:
Its seems a pity to waste energy heating the water up a high temperature (with reduced heat transfer efficiency as the water gets to higher temperatures) , only to cool it down with cold water from the thermostatic valve.

It does, a valid point.

The reasons are that the hot water should be generated/ stored ( if storage is involved) and circulated at 60 degC. Any lower and you risk propagating unfriendly bacteria (legionella) in parts of the distribution system. Any higher and you get more lime scale problems in hard water areas. The water at the outlets should be not more than 46 degC, to avoid scalding young children.

This results in storage at 60degC and thermostatic mixing valves at the point of use. That's the way the NHS have done it for years. If you can devise a better or cheaper way they (& I) would like to hear of it.

croydoncorgi · 12 Jul 2006

If you take 5 litres of water at 60 C and add 5 litres at 20 C then you get 10 litres at 40 C but no heat is wasted !

Yes - but your combi will definitely go out of condensing mode if required to deliver water at 'high' temperature, so it IS more wasteful.

This issue of legionella in pipes is over-stated if there is no tank. For a start, the water will be at higher temperature now and then, so the pipes get 'sterilised' (well - not in fact but adequately heated) often enough to remove any risk.
IMHO, TMVs at point-of-use are a Big Mistake except in high-risk situations (care homes, etc). They need maintenance and they often don't work properly. I took one out only yesterday because it was incompatible with a bath mixer: you could have hot or tepid to cold but nothing in between! Call me incompetent if you like but it was just not worth fixing. I reckon the design was crap anyway (not to NHS TMV spec) and it was in a houseful of entirely 'abled' adults.

But to answer the original question: remote control of HW temperature on a combi? Forget it unless the boiler has Opentherm (eg. Keston C36). You would iimmediately invalidate any safety certification that the boiler has to have if you modified the controls.

simond · 13 Jul 2006

I believe you can alter hot water setpoints on a Vaillant ecoTEC plus combi fitted with a VRT360 or VRC400 remote controller.

Also on a Viessmann 200 series combi fitted with their remote controls.

Both these boiler controllers can also set the dhw temperature (in their system boiler variants) when used with their own unvented cylinders and thermistors.

I'm not aware of a way (within the construction and use of the product) of doing this remotely with a Worcester 35CDi product. This is probably because their controls do not currently feature a bidirectional data bus, although I have a feeling their new text display may use one but we haven't fitted this controller yet.

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Remote control of boiler DHW setpoint

breezer

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