Just back from being away for two weeks and thought my water pressure was a bit low. I phoned the waterboard in case there was some known problem. Thy said no.
I realise now that the cold is okay but the hot is a low.
I have a Worcester Bosch Greenstar Combi. Is there anything I should look for?
Roger Mills wrote in news: snipped-for-privacy@mid.individual.net:
How? Does the boiler moderate the flow in some way? I don't remember it last winter.
Summer? The flow will be higher when it doesn't have to raise the temperature so much!
Yes, the boiler controls the outlet water temperature. If it's not hot enough with the burner on full, the only way it can make it any hotter is by slowing down the flow.
Not sure about this model but some have a "temperature" knob; turn that up and it reduces the flow (like an electric shower). Do you have an OH who might have got at it?
It is in the loft - and the controls are under a cover. She would have absolutley no interest in even going near it. So the view is that intial temp setting is by flame height - if that can't meet the target set then the flow is reduced. Logical - but is mine really like this?
Hopefully a simple example. Assume you want hot water at 50C.
Assume the boiler can raise the water temperature by 30C when going full blast and full water flow.
In the summer the incoming cold is 20C so it raises the water to 50C going full blast. A rise of 30C.
In the winter the incoming cold is at 5C, so at full blast full flow it only raise the water to 35C. A rise of 30C.
So the only way to increase the temperature of the incoming water is to reduce the flow so that the same amount of heat is used to heat less water. With a target of 50C it has to slow down the water flow quite a bit. (I would guess to 75% of full flow in this example).
HTH
Dave R
A flow of 10 l/min and 30 C temp rise requires 20.94 kW.
A flow of 10 l/min and 45 C temp rise requires 31.4 kW. A flow of 6.5 l/min and 45 C temp rise requires 20.41 kW.
Close enough. B-)
Can the OP's boiler actually modulate the water flow? I've not come across a combi that does - but then I only come across older combis in friends houses etc.
I think it must do. If not, he'd have reported a different problem - with the water not being hot enough.
Must it? Perhaps he didn't notice a temperature change.
Do boilers modulate the flow? If they do, know body has said so.
It seems like an unnecessarily complication to me, after all the user can reduce the flow by not turning the tap on as much or get full flow albeit at a reduced temparature. Their call.
I cannot see anything on the schematic diagram that implies any mechanism for reducing the flow.
However a thermostatic mixer shower will reduce the flow of cold to maintain the required temperature if the incoming hot water is not up to temperature - especially if the incoming cold is very cold.
I have no idea if it throttles the hot.
What I have observed is that with our thermostatic mixer it runs very slowly until the hot water comes through then speeds up a lot. I assume this is because it shuts off the cold until the hot water needs some cold adding to it.
Cheers
Dave R
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