What's a typical cause when a boiler starts to require increasingly high demands for hot water before it decides that it should light up the burner to deliver it?
My guess is that there's a pressure drop valve, and that it has become stiff or its seals have become sticky.
Daniele
In my (limited) experience it is usually a flow valve. Which is easy to replace if you can get at it at all.
Mine has a turbine with a coupled magnet and a Hall sensor.
The turbine runs in water and a while ago mine stopped turning because of some junk. Easy fix, once I found how to access it.
Some use a valve (with a magnet) that moves away from it's seat once there is a flow and is sensed. Obviously the position of the sensor is critical.
On our multipoint gas water heater there is a water pressure detector valve that is linked to a gas control valve via a small stainless steel push rod and on my first MPWH a slight leak there caused corrosion and so to stick (and eventually stuck) the interaction between the two.
I removed the water side, released and cleaned the pin, replaced the O ring and re assembled it with some suitable silicone grease and it was fine for ages after that (till neighbour got rid of his later one and we upgraded ours). ;-)
No idea if that's how they work in combi boilers (might be in the older ones)?
Cheers, T i m
Yup, there are a number of different ways that they can detect the DHW flow. Some use pressure drop valves or diaphragm switches, some direct flow detection switches etc. Hard water scale can make many of them less sensitive, as could diaphragm deterioration etc. What make and model of boiler is it?
It's a Baxi 105 HE.
I realise I have actually replaced the diaphram before. It seems to move smartly enough, it's not sticky, it just seems to move only when there's more pressure than it should need.
Daniele
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