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I've added up my radiator output, it's roughly 12 kW (suggesting the rads are perhaps slightly undersized for the house). It seems madness to recommend a 30kW boiler, I guess they're basing it on the current boiler being a 28kW unit. I've asked the person supplying the Vaillant quote about...

I don't know more than expert, I don't want to know more than experts, but I do want to know enough so that I don't get caught out by a numpty who doesn't know how to size a boiler! :lol:

Your advice is very much appreciated, hence why I also pressed the thank button for your earlier response! Depending on who you ask my 20% is conservative, Danfoss claims up to 40% improvement from WC :shock: Guess it's the double-edged sword of marketing lies and internet. I came into this...

I do get the feeling I'm over-thinking this all. A condensing boiler that's not condensing should be as efficient as a regular boiler, right? So that's 80% instead of 90%? So all this fancy controls logic etc is trying to ensure that it's spending more time at 90% rather than 80%? That...

I'm even more confused now.... Thought I'd get the information straight from Vaillant, emailed them for confirmation. Got the following response: So now the Vaillant technical support people are saying their supposedly advanced controls offer no benefits over a simple on/off roomstat +...

I'll see if I can get some alternative Vaillant installers to come round for a quote, see if I can find one who's done a vr 65 install. I guess Worcester Bosch doesn't have anything equivalent? Their own intelligent controls all state not compatible with S/Y plan systems?

I guess my other limation is with the Megaflo and VR10 NTC which don't seem to go together well. The vr 65 docs suggest that VR10 NTC is optional, so I guess could live without it for now? Could decide to rip it out in the future and install Vaillant's own alternative.

Hi UpgradeME, I'm glad I'm not the only one stumped by this. This has to be a very common problem? Do people really just not care about boiler efficiencies? I too assume the boiler will do some sort of modulation on return temps to try and keep it condensing, but with the system boiler...

The current setup was fitted at the time the house was built, 5 or 6 years ago so I guess the building inspector was happy to sign off on it. I bought the property recently but from what I've seen so far, the builders were a right bunch of cowboys. I really would feel better if a new supply...

I've recently received several quotes to replace my current system boiler as it repeatedly failed over the past winter. 4 bedroom detached house, system boiler in the garage, megaflo cylinder upstairs. Online heat calculator suggests 14.5 kW heating required. I received quotes suggesting a...

Excellent call, I think I have found my gremlin in the system. I can't even begin to think how this is supposed to work. Tested frost stat (it's labelled Potterton) using multi-meter. Ambient temp around +5C or so. Set the frost stat to -10, it's calling for heat (verified, 220V on...

I had a poke about with the multimeter today. External controls voltage is at 0 when the valves are shut. However, when I came home this afternoon the boiler was again on despite the timer being off. I wasn't quick enough with the multimeter to see if an external control was asking for heat...

I was looking for something like that, but haven't found anything like it. There is a control block (a many-way sugar cube block) next to the boiler that the frost thermostat (and a number of other wires) are connected to, with the output going to the boiler. I'll see if I can get my hands...

I had the boiler serviced recently and the frost stat setting was changed from -5 to +5C. I believe at the time the valves were also prodded and they looked ok, but I'll double-check. If a frost stat kicks in, should it also open the CH valve or just make sure that the pipes are hot?

Hi all, Our newly purchased house (modern construction, 5 years old) has an odd problem. Potterton Performa 28E system boiler, fitted with Myson room thermostat and 2-channel timer, feeding rads and a megaflo hot water tank. Timer controls 2x 2-port valves installed below the megaflo (I...