Help diagnosing (& hopefully fixing!) a hot water supply issue

vacheron

BeeTheGoddess said:

vacheron said:

Looks like you have a 3 position valve setup with a tank thermostat. 

There are therefore 2 likely problems if the hot water works when the CH is on. 

1: The tank thermostat (the one with the rotary dial cut into the foam of the tank) is set far too low, or isn't working. This turns off the hot water when the tank reaches temperature.  From the picure, if the indication is at 6 o'clock, the dial may be set to turn off at about 20C so the HW will never come on. Turn this up to about 60C if this is the case. 

2: The three position valve (second last pic with the two black arrows on) is faulty . These can be pushed into position manually to test them, but they regularly fail These also call the boiler to heat, these are pushed one way by a motor and retun using a spring, so if it cannot move (valve is stiff/seized) or the internal motor drive or one of the internal microswitches are faulty, it cannot call the boiler to fire.  

 

OH MY GOD I THINK YOU FIXED IT YOU ABSOLUTE SAINT!! I thought the indication was 12 o'clock where the 60c is currently. Made 60c at 6 o'clock, turned the hot water on and the boiler responded!!!!! Just waiting to see if hot water actually appears, but now feel really draft for not spotting that hehe. 

Ah that's great news. Fingers crossed! 

Another way to test things are working is to carefully touch the three pipes leading to and from the 3 position valve in the second last photo. you should feel warm water entering from the pipe at the back and leaving to the right while the left (CH) pipe should be relatively cold (it may take a while for the pipes to heat up though if the valve is on the return path from the tank).

vacheron

Rodders53 said:

Albermarle said:

If the hot water thermostat was set too low, then the hot water should not have worked when the CH came on or when the Immersion heater was on? 

Immersion will have its own thermostat under the metal cover!  Completely separate from the tank strap on stat.

Valve could be letting-by when in CH position to still give some flow through the tank heating coil?  

The reason for my guess was that the OP may have a thermal store whereby hot water is flash heated by passing mains pressure cold water through a coil surrounded by the hot (dirty) central heating water (as opposed to a conventional system where the dirty hot water from the boiler passes through the coil and heats the water in the surrounding tank).

This allows large amounts of instantaneous mains pressure hot water but requires the water in the tank to be heated by the boiler first. This will happen automatically whenever the centeal heating is running because the central heating water passes from the boiler through the tank first before going through the radiators. 

It also means the OP should rarely need to run their DHW in the winter, but will need to give the hot water a boost in summer as and when required. 

danrv

BeeTheGoddess said:

danrv said:

Is it a Honeywell motorised valve? They have been known to play up. Tend to get hot due to lack of ventilation.
Maybe try resetting the programmer but it sounds like the MV microswitch isn't waking up the boiler as it should.

What's an MV microswitch?

Motorised valve microswitch. 

BeeTheGoddess

This is all getting gloriously technical & I appear to have solved the problem, saved money, and learnt more about how boilers work. Thanks very much everyday, much appreciated. 

zenshi

I’m going to investigate my dials as I have exactly the same problem and also have Honeywell programmer