Combi's (Accepting Pre heated Mains water)

[Water Systems]

Sort of... I've put a tank stat in circuit with the boiler water demand switch , it makes the boiler think that the water is not being drawn when the cylinder is above the set point (about 45°C) and stops it firing.

Thats a very clever solution to the dead leg problem when there is sufficient hot water!

How I understand that, is that the internal wiring of the combi boiler was broken into.  If so, this is frowned upon and would invalidate a guarantee.  However, done by someone who knows how it works, it will work fine.

[martin W]

Yup, it would invalidate a guarantee. But the combi (in question) is well out of warrentee, the wiring run though a cable gland in the bottom entry plate of combi then though conduit to the switch (all nice and tidy). Obviously if you don't know what you are doing, and can't route and terminate the cable safely ... don't do it.

I can't really think of any other way of interupting the combi' other than placing a relay on the power supply of the combi, so that it is turned off when the water is hot enough from the solar. The only problem I thought of with that method, is that the water could be hot enough and turn the combi off but I might need central heating (my water will be heated by solar and also a wood burning stove). With this scenario in mind I decided to interupt the signal which told the combi that water was being drawn off.

I suppose you could route the live feed from the fused spur though a tank stat (pipe stat), then on to power up the combi. At least it would not invavlidate any warentees, and unless you wanted heating when you already had hot water (form solar/wbs), this would probably be the best solution.

The wiring in my case was altered by using crimp connectors - 1/8" spade type. These were already in exisitance in the boiler inside the water demand micro switch. SO other than the extra hole in the base place for the cable gland the whole unit can be easily put back to factor specs.

[martin W]

Any1 know if a Baxi Combi 133HE plus can take pre-heated water?

cheers

UPDATE: Just got off the phone to Baxi service and they said upto 50°C would be OK for this boiler... if it went higher than 50°C they would expect me to have problems with cycling of boiler and lock outs.

[pete_w]

Just thought I'd revive this thread.  I was reading the owner's manual for my boiler (Vaillant ecoTEC plus 428) and it has this odd little bit in it that described a user-selectable function "d.58: activation of solar reheating".  I'd seen it before and never known what it was.

It's a slow afternoon so I looked for the ecoTEC plus manual in its native German, and it's a bit more forthcoming about this mysterious d.58.  My dodgy german (and google's dodgy translation) appears to suggest that it does exactly what you're looking for - reheat of solar-preheated DHW up to 65C.  There's a warning note earlier in the manual that incoming water must be at 70C or less or else the equipment may be damaged, use a mixer valve if necessary.

I'd urge you not to take on trust my dodgy translation of a foreign-language manual for a product for a foreign market, but it does suggest that if someone perseveres with Vaillant's UK tech support (good luck with that...) to get an explanation of this feature then it might be another one for  the list....

None of this affects me, I'm a thermal store user not a combi boiler user, I just pass it on.

Cheers
Pete



 

[tris1331]

That's very interesting pete_w.  I know how frustrating their technical department can be, when you finally get through! 

I'm on a course with them on 2nd June so will quiz them about d.58 and will report back.  Does anyone want any specific questions asked?