Worcetster bosch greenstar heatslave 18/25 frost protection

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Hello, i'm new here. This is a great forum, i wish i found it sooner!

We have had the above condensing combi oil boiler for nearly two years now - fitted in an unheated detached garage. During the recent cold weather the boiler was running most of the time day and night resulting in excessive temps in the house.

I researched the problem and deduced that i should be fitting a low limit pipe stat on the CH return pipe and wiring it in series with the frost stat.

I got the parts i needed from the local plumbers merchant and set about tracing the wiring circuits of our boiler and controls. We have a drayton timer switch for DHW in the garage and a drayton digistat +2 programmable room stat for CH in the house.

I then realised we had two frost stats wired to the boiler. On reading the boiler manual it says that this boiler needs two frost stats wired with a shared permanent live and the switched live from each stat going to two seperate terminals on the boiler PCB.

I was then confused so decided to call worcester. They said the pcb was designed to be used with a double pole frost stat and because they are no longer available this is why 2 frost stats have to be used. I asked how should i wire up the pipe stat and they said just take out one of the frost stats and replace with the pipe stat.

Ok i thought but this means the two stats are in parallel not in series. I wired it up as worcester recomended and waited for the temp to drop. With a digital multimeter i deduced that even when the return temps were above the 20 deg C i set the pipe stat at, the frost stat was still turning the heating on. Also when the air temp was above 5 deg C and the return temp below 20 deg C the bolier was coming on.

*******s i thought. I have now disregarded worcesters advice and wired the two stats in series (frost stat to pipe stat) with two switched live wires taken from the pipe stat to the two connections on the boiler PCB.

Tested it and it is running flawlessly. Boiler is still frost protected and it does'nt run all bloody night any more. Result.

I believe worcester gave me wrong advice and why did'nt the installer (worcester accredited installer) work out that i would need a pipe stat? Does'nt fill me with confidence really.

Regards, stu
 
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Worcester will cover their ass's as will their engineers, I have many times come across their engineers works (4 engineers to fault find on a worcester Heatslave, & couldnt find the fault ... yet I diagnosed & fixed in 30 mins)it was the firevalve at fault, HOWEVER this is where you have to be careful, ANY work carried out without "permission" of Worcester may lead to them invalidating their warranty, just make sure the frost stat is set @5oC as it is a common misconception that it should be set @ 0oC water starts freezing @5 & is solid @ 0oC, but if it's working GREAT :D
 
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Thanks for your reply djsarge.

Yes frost stat is set at 5 deg C . Pipe stat is set at 20 deg C - is this ok?

I realise going against their advice may invalidate the warranty but the advice i was given by worcester ( i pretended to be a qualified installer) was clearly wrong as it did'nt work.

Also i suspect that my diy wiring may be illegal but i am not a complete novice. I have checked and tested multiple times. If we ever sell up it is easy to put it back to the original set up.

As far as a manufacturers warranty goes i dont think they are worth the paper they are written on. When i bought a 1 year old car i decided to do all the servicing myself and sod the over inflated charges needed to satisfy what was left of the warranty. Car is 12 years old now and still going strong.

Thanks again, stu.
 
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yes thats fins Stu, & totally agree with the servicing the car yourself I do the same!!! :D but since you have to call an electrician in these days to change a fuse, I can see why you did the electrics yourself though!!!& the ONLY warranty i'd buy is the Grant Extended warranty ..that appears to be the only one,
But god luck & I'm glad all is working well
 

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