Small volume of hot water

[Tony_P]

I’ve a conventional gas boiler and unvented water tank which is probably about 500l; it’s two mètres tall and about a meter across.

I get good hot water pressure at a good temperature (it’s set at 60c) but only enough to fill about 10cm of the bath before it runs cold.

Does anyone have any idea what could be causing this? I had a plumber visit who suggested that the main volume of water in the tank isn’t what’s being supplied to the taps, but rather there’s a coil inside the main tank through which the hot water runs to get heated. Is this possible, or likely?

The house is a five story Victorian terrace with five bathrooms, so a system that only supplies such a small amount if hot water seems strange. The boiler’s a 45kw unit, so well capable of providing enough.

The boiler’s in a mews block at the end of the garden with a flat above, so conceivably there was a smaller capacity setup for the flat which someone has then switched for the main house, but does that seem possible?

 

[John.g]

Presume pump(s) heads are important after looking at this?.

 

[Jerry]

I spot 3 pumps but no zone valves?

 

[Tony_P]

I spot 3 pumps but no zone valves?

The zone valves are in the basement of the main house.

 

[John.g]

The boiler circ pump feeds one "side" of the LLH, there will be another pump to distribute the water to the different zones presumably, can you give details of this including make/model/settings and check that it's actually running when HW cyl coil motorized valve is opened.

 

[Tony_P]

The boiler circ pump feeds one "side" of the LLH, there will be another pump to distribute the water to the different zones presumably, can you give details of this including make/model/settings and check that it's actually running when HW cyl coil motorized valve is opened.

Hopefully these are the right ones.

 

[ShaunCorbs]

Needs a commercial engineer to have a look and diagnose

 

[Tony_P]

Needs a commercial engineer to have a look and diagnose

Yes, I had one this morning that I am not sure was correct in his diagnosis, so I'd hoped someone here may know.

I'm struggling to find anyone capable of diagnosing and fixing the issues.

 

[John.g]

If the cylinder coil is supplied from the secondary side of the LLH then the hot water temperature can vary a lot depending on the ratio of primary/secondary flows, the greater the secondary flow rate the colder the secondary flow temp due to dilution from bypass from the secondary return.
The coil may be supplied from the primary (boiler) side?, you could check this by looking at where the coil flow and return are teed into the system.
Did you carry out the bath test yet? and how many rads in the system?

 

[ShaunCorbs]

Yes, I had one this morning that I am not sure was correct in his diagnosis, so I'd hoped someone here may know.

I'm struggling to find anyone capable of diagnosing and fixing the issues.

What was his diagnosis and was he a commercial gas / plumber ?