Conventional boiler - no hot running water but heating fine

[prophet]

Afternoon all

I have a conventional heating sytem with conventional boiler and hot water tank.
Though the central heating is working as it always has, piping hot, the hot water coming out of the taps has, over time, become less hot anad is now pretty much cold.

Before I get a plumber involved I was hoping there might be a few things I could check which might resolve the problem. Any ideas would be gatefully received.

See the below attached images of the tank layout:

 

[Bonni]

Possibly a diverter value issue.

 

[Hugh Jaleak]

It appears, from what I can see, you may have a very primitive Fully Pumped system, with manual control on the CH side rather than Motorised Valves as would be expected. Assuming the feed from the pump goes horizontally to the Radiators, with the vertical spur feeding the Coil on the cylinder, and a Gate valve to control the flow to the Rads.

If this is indeed the case, I would seriously suggest you get it upgraded to a 'S' or 'Y Plan' system with the use of Motorised Valve(s) and Thermostats to control the flow of water from the boiler and best utilise the available output, especially given the current fuel price situation.

The current issue with poor hot water, could simply be a blockage in the pipework, preventing circulation, which would require affected pipework to be cut out and replaced. I would start by running a magnet along the pipework between the pup and the cylinder, see if there is any sign of it attracting, which would indicate a blockage.

 

[prophet]

Thanks for the replies.

New information:
So, hot water from the boiler is entering the cylinder but is cold on the return.
Logic suggests that it isn't continuing through the cylinder coil else it would heat up the surrounding water. Or is my logic flawed and there's another explanation?

 

[Hugh Jaleak]

Is that air vent in the first picture connected to the flow into the cylinder coil? If so, open it and see if any air escapes, could be as simple as air locked pipework. If not then do the magnet test. Might be a tiny trickle of flow, enough for the pipe to get hot, but not enough to transfer any significant heat into the cylinder.

 

[prophet]

Yes it is. I bled it before starting posting but there was no air.
Magnet test?

 

[oldbutnotdead]

Yes it is. I bled it before starting posting but there was no air.
Magnet test?

Get a powerful magnet, run it over the primary pipework between pump and cylinder especially at any elbows, tees, bends. If it sticks there's a buildup of ferrous crud in the pipes.
Also given the lack of motorised valves, it might be worth turning all but 1 radiator off then firing up the heating (increase the pressure differential across the coil).

 

[gas112]

The gate valve in pic`s 3 and 4 on the pipe back from cylinder without wheelhead on it , could have some crude in it restricting the flow through cylinder so gently close it then open it around two full turns

 

[prophet01]

I thought it was a bleed valve but others more knowledgable referred to it as a lockshield.
So a lockshield gatevalve key is required.

Is there an easy way of ascertaining the correct size?

 

[prophet01]

Thank god for phone camera technology.
Topside and underside of the valve indicate the following info.
PN20 and 15mm

I assume the 15mm relates to internal pipe diameter but not sure about the PN20.
...Google says nominal flange pressure.

So no clue as to the key size required.

Any ideas

 

[Jajodu]

Look like a stopcock with the handle missing to me.

 

[prophet01]

The gate valve in pic`s 3 and 4 on the pipe back from cylinder without wheelhead on it , could have some crude in it restricting the flow through cylinder so gently close it then open it around two full turns

@gas112

Good call dude. No key required. A few sharp taps with my rubber mallet and I could hear the flow.

Great result. Hot water flowing out the taps.

Thanks to all who contributed. Really appreciate it.

 

[fixitflav]

@gas112

Good call dude. No key required. A few sharp taps with my rubber mallet and I could hear the flow.

Great result. Hot water flowing out the taps.

Thanks to all who contributed. Really appreciate it.

Probably not something you'll worry about if it's been that way for years, but according to the Grundfos data the control box can be in any position except where yours is, directly below.

 

[gas112]

that pump is over 30 years old so i would not worry about its orientation

 

[fixitflav]

that pump is over 30 years old so i would not worry about its orientation

Yes, that's why I said I didn't suppose the OP would worry about it.