Why is the "hot" water in my taps and shower only

[grizzlybiker]

My combined (not combi) gas HW+CH system has been working with no problems then suddenly, last week, the "hot" water coming out of the shower and all taps is barely warm. The gas boiler and the programmer lights are on.

It seems that the HW is being partly heated but not anything like hot enough, compared to how it normally is.

I have not touched the surface mounted HW-cylinder stat so it is still set at 65c.

The CH radiators are all nicely warm.

When I turn the HW switch OFF at the CH/HW programmer, I hear a sound like the m/v is operating and I can feel the pipes either side of the HW m/v are very hot.

When the gas boiler is on, the HW cylinder now does not feel hot at all but tonight, when I turned on the electric (back-up) water immersion heater, I got hot water in the shower and taps within 20 minutes.

 

[seco services]

check the cylinder stat is not faulty and cutting out to early

 

[JohnD]

and how hot are the pipes, going in and out of the side of the cylinder, carrying the primary heat from the boiler? Are they driven by a pump, or gravity flow?

how well insulated are the pipes and the cylinder?

 

[grizzlybiker]

Seco and JohnD, thank you for your comments. Hopefully you can see my picture below.

The pipes are not insulated as they are in a warm airing cupboard. The water pipes to and from the boiler to the HW cylinder were both cold.

I replaced the surface mounted H/W cylinder thermostat, as suggested, then I removed the motor part of the HW m/v (the upper one in this picture) and then I opened and closed the HW valve manually. I then increased the new stat up to 80c and the boiler powered away and has now given me a full tank of hot water for the first time in a week.

I am monitoring the situation but I am puzzled how the issue has been fixed (probably it is only temporary). Maybe the HW m/v "got stuck" and the whirring noise incorrectly led me to believe it was working correctly ?

Could you tell me:

(1)

Can you see from the attached, what is the purpose of the gate valve ?

(2)
I assume that the m/vs are closed when the valve fin (after removal of the motor part) is in a vertical position and it is open when the value fin is horizontal ? I am I right ?

(3)
Is the pump kind of "sucking" water from the boiler then "pushing" it through the M/vs to the HW and CH respectively ?


http://s630.photobucket.com/albums/uu28/headache5678_photos/?action=view&current=IMG_4855.jpg

 

[grizzlybiker]

Thank you - I installed a new surface mounted thermostat, then opened the vent valve near the top of my cylinder. This released a huge volume of bubbling air - like when one bleeds a radiator but the process lasted 20 minutes and was much louder. Now my HW is very, very hot. It is fantastic. Thanks guys. I still don't understand what the gate valve, in the picture, does.

 

[ajrobb]

Is your hot water cylinder unvented or is it supposed to be vented to a cold water tank?

 

[grizzlybiker]

AJ,

Er - I don't know - does the attached picture clarify ?

http://s630.photobucket.com/albums/...os/?action=view&current=Pipework2IMG_4831.jpg

 

[seco services]

the gate valve is a bypass.
so when both valve are closed the water can pass back to the boiler.