Conventional gas boiler not fully heating water

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I’ve an Ideal Classic 50 conventional boiler : pumped radiators, gravity feed to hot water cylinder. It was last serviced September last year.

over the last couple of weeks I have noticed that the hot water produced is nowhere near as hot as it was. Three weeks ago I would have to add cold water to a sink full, for washing. Today, no cold needed at all and the temperature, I would describe as simply tolerable.

the radiators are hot, no problem on that side.

What’s going wrong?
 
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Can you try turning off the central heating for a while and see if the boiler is coming on at all just to heat the cylinder.

Some pictures of the system and the programmer would be useful.
 
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With the heating off, the hot water does carry on being heated
The programmer is a Potterton EP2001.

I’m not sure what a thermostatic shower or taps is, but our shower is just one that goes over the bath mixer taps and fed from the cylinder (hot). and mains (cold), all other taps are just plain old taps

one other thing worth noting is that the small radiator in the bathroom is fed from the same gravity feed as the hot water, as a result it has never been as hot as the main radiators, but that too is much cooler than it used to be.
 
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1. I suspect you have a fully pumped system, otherwise you wouldn't need a two channel programmer, which is what the EP2001 is.
2. If I'm right:
2a. You will have either 2 x 2 port motorised valves (S Plan system) or 1 x 3 port valve (Y Plan system) AND
2b. A thermostat attached to the hot water cylinder, normally about 1/3rd the way up from the base.
2c. The motorised valve which controls the flow of water to the hot water cylinder primary coil may be faulty. OR
2d. The thermostat has been set to too low a temperature, or is possibly faulty.
 
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Is there a temperature setting on the boiler, perhaps it needs turning up? Turned down during the service.
 
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Water is freezing at the moment, how long is you HW on for in the morning?
 
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The hot water is definitely gravity, I remember the engineer telling me that when he was explaining that the hot water will always be on while the boiler is on (which it is). The boiler manual shows this to, explaining that there are 4 pipes coming out of the boiler, two for pumped, two for gravity - all are connected. There is no thermostat on the cylinder.

the system comes on at 05.30 the boiler control goes from 0 to 5 and is set to 4 which heats the radiators to around 59 degrees
 

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What colour is the hot water cylinder?

How far is it from the boiler?
 
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Well, that certainly seems the obvious action to take (turning it to 5), but I suppose my point it that in the years we’ve had this boiler there has never ever been a need to turn the temperature up beyond 3.5 before and the water has been piping hot. It just seems odd.

iknow that at 18-20 years old the boiler could probably need replacing, which is being considered this year. But it doesn’t explain why it’s just the water that’s not getting as hot as it used to, so I was wondering if there was anything I could do or if these symptoms spell out an impending problem
 
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The cylinder is copper with a good thick insulated jacket. It is in the airing cupboard directly above the boiler - literally 2ft from top of boiler to base of cylinder
 
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The cylinder is copper with a good thick insulated jacket. It is in the airing cupboard directly above the boiler - literally 2ft from top of boiler to base of cylinder

No partially closed valve between them?
 
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I can’t see any type of valve but no idea what’s under the bathroom floor - certain nothing I, or anyone else, has touched in 18-20 years
 

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