A friend (as in the Flue question) has had a combi fitted upstairs (new flue through roof). The fitter did a great job, but the electrician needs to come in 2 weeks after my friend returns from holiday - therefore it is running without a room stat at present.
He is concerned about the noise and some of his family have switched it off at the spur unit. My instinct is that this is a bad idea as it could upset the pump or fan control. However, what is the noise - is it a fan?
Shouldn't cause any problems -- boilers have to survive the occasional power cut. I wouldn't switch it off this way too often when the burners are alight though, as it may cause localised boiling and overheating of the heat exchanger when the pump suddenly stops.
Um, how could we possibly tell?
No problem - if it's like mine. It comes with the thermostat wiring bypassed anyway.
You can hardly hear mine at all with the cover on. Apart from when it first starts - I think it blows air fast though the flue to make sure there is no gas in there. But it's not a combi. The electronics are fine if you power down completely - it will remember all the settings.
That's interesting. The fan failed on my 3 year old WB combi boiler, which I discovered immediately when I returned from holiday. The engineer (one from WB) told me not to switch it off *ever* at the main switch since the boiler needs to perform self tests every 24 hours and (the switching off) may have caused the premature fan failure.
I'm not saying I believe him. I am just reporting this since the WB engineer *should* know what he is talking about.
I'd agree with him - although not necessarily word for word. My Viessmann runs the pump for a short time every 24 hours even with heating and water heating shut down to prevent it seizing. There is a standby button to achieve this state as well as a normal mains isolator on the boiler.
Why should the fan be liable to seizing up when not in use unless it's faulty? After all the fan is not use for quite a while between manufacture and installation.
That's why I said I didn't agree with him word for word. But do with the principle of leaving the boiler powered up - if it needs it. The installation instructions should make it clear whether this is needed.
It could be the pump. As the thermostatic valves on the radiators close, the pump faces increased resistance (or something). It will start off quiet and get louder as the house heats up if this is the case.
The thermostat circuit could be low voltage in which case you could do it yourself:)
He was running it with only DHW selected. His son got up in the middle of the night to switch it off due to the new noise in the house.
Assuming a modern Viessmann (I only have details of my one) the pump is a vary speed unit so will adjust. It also has a built in bypass loop.
Mine uses a room temperature sensor rather than a thermostat. So all adjustments are done from the programmer. But it has the option to use a conventional one.
The user and the installation instructions make no mention of leaving the boiler switched on.
I must admit to being confused here. Either there is a risk of seizure to the fan if switched off and therefore it must be left on or there is little/no risk and hence it does not matter whether it is left on or not?
There are two sources of noise the combustion fan and the circulator. When on standby these may operate.
Most modern boilers seem to have an anti pump seize feature. Some pumps when they get older can seize up if they are left for several months. Once a day is probably OTT to ensure that the pump does not seize but IMHO it must add some reliability. Older systems where the pump is only used for the CH did have a habit of seizing over the summer.
However the most likely cause of significant noises from a combi when not in use is some sort of warm standby mode. It might also be that the customer has not been fully informed about the way the boiler works etc.etc. And are inclined to believe that off should mean off and are thus concerned about the noises.
I'm unaware if any boiler has an anti seize feature for the combustion fan, these rarely seize, in my experience, anyway, so far.
In general the only boiler that I know of made in the last 15 years which was intended not to be connected to the mains 24/7 was the baxi barceona. A number of features require permanent power
Frost Protection Built in time clocks. Anti seize feature. Warm stand by feature.
In message , Ed Sirett writes
because pumps can seize by scaling on the shaft - a quick flick keeps this at bay
fans seize when the bearings have come to the end of their life dead jim
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