Heating works very slow recovery on DHW pipe design question

[cjd10]

Three story victorian house - Boiler OK recently serviced, central heating hot, no cylinder stat or valve, system is fully pumped

DHW very very slow to recover

Clearly flow from the boiler to cylinder is an issue, strangely is has 22mm entry into the HW cylinder heat exchanger but only 15mm return back to the boiler. is this normal?, I would have expected a 22mm return??

thoughts anyone

 

[gas4you]

Sounds like the installer has used 15mm to act as a restriction to balance the hw cylinder with the rest of the system.

This has been done quite a lot in the past and should not on its own cause the problem you have.

What floor is the hw cylinder on? Is the system full of water an the F&E tank full up?

Sounds like there could be an air lock or possibly a slight blockage in the dhw circuit.

 

[cjd10]

Dave

thanks for the quick reply

the Cylinder is two floors up from the boiler (its in the cellar)

The F&E tank is full, system is full of water

your right, Air lock and/ or blockage looks to be the most likely

chris

 

[Gasguru]

Is there a manual air vent on the top cylinder coil connection?

 

[gas4you]

Is the pump next to the cylinder or at boiler level?

 

[cjd10]

A U bend of 15mm pipe attached to the top of the top cylinder coil connection that goes north to the attic,

Pump is at the boiler level

 

[Gasguru]

Appears to be a cheapo job. Have you checked the feed tank in the roof has sufficient water?

The inverted feed pipe could be blocked. However air could still be trapped in the coil since it would have difficult rising up the the tank.

I assume you have to turn all the radiator valves off if you don't want the heating on and set the boiler thermostat half way to avoid scalding hot water.

 

[gas4you]

Strange set up

Check for air bleed point on this pipe in attic.

Could possibly be pump is giving up the ghost and has not got enough power to circulate this high anymore.

I would fit a 15-60 pump on an installation like this.

 

[cjd10]

I will try and find end point on this pipe

Pump is new Grundfos 6m

Feed tank has sufficient water

The central heating has a zone valve the DHW circ is poor with this valve closed or open

 

[gas4you]

F&E tank should be at least 1M above the highest point/pipe work in your system. Is it?

 

[cjd10]

yes must be approx 2.5m above tank

 

[Agile]

Whats are the flow and return temperatures at the boiler and at the cylinder?

Tony

 

[holty]

what boiler is it?

 

[cjd10]

Its a robust P kingfisher not green old but bomb proof, recently serviced, central heating hot and efficient

re other post flow temp at the boiler hot, flow temp at the imlet to cylinder mostly hot, sometimes cold, hot flow then going up the vent and fill pipe!!!

flow outlet from cylinder cold (but gets hot after a very long while) cold into boiler but gets warm after a long while


note cylinder new about 5 years ago,

 

[ChrisR]

see if water is "pumping over " in loft when hw is on.
SOunds like an old gravity system badly converted to fully pumped.
Is that the only open vent the boiler has? If so it's "illegal".

Can you post a pic of this "U bend"?

Cheshire - so not hard water areas then? Cylinders can block.