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

On 18 May 2021 at 12:01:08 BST, "D.M. Procida" D.M. Procida wrote:

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.

--
Roger Hayter

On 18/05/2021 12:01, D.M. Procida wrote:
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.

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 Tue, 18 May 2021 12:01:08 +0100,
(D.M. Procida) wrote:

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.

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

On 18/05/2021 12:01, D.M. Procida wrote:

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.

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?


--
Cheers,

John.

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John Rumm wrote:

On 18/05/2021 12:01, D.M. Procida wrote:

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.

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