hot water is not heating up quickly anymore

[graham964]

I have a problem which has shown up recently with the water heating or lack of it.

The system I have is a pressurised combined water and central heating system. It comprises a standard ch pump which feeds 11 radiators, a second pump and controller which feeds an underfloor room heater and a water cylinder. All of this is supplied by a Potterton boiler. The underfloor heating was supplied in the March 2009 and after a few teething problems (the plumber connected the feed to the second pump to the wrong side of the existing pump which prevented it triggering the new pump when required) I think it was all ok from here but I cannot be sure that I ever ran the whole system together (rads-underfloor and water heat). Assuming that this is OK then why does it now take even with central heating turned off nearly 12 hours to heat the water? (It used to take about an hour and was pretty noisy in the process)

I suspect the mid position valve which may not be opening fully and restricting the flow through the hot water cylinder. The reason I suspect this is that the boiler comes on for a while (no call is been made by the central heating or underfloor) but it only stays on for a short while (a few minutes ) .
Any ideas , comments or suggestions on what I should do are very welcome.

regards

Graham

 

[twgas]

Has the balancing valve, if there is one, on the HW been turned too off?
The only other things are; connected wrong (especially if it hasn't worked since other work done), or a restriction in the pipework, either sludge or air (has it been bled)

 

[graham964]

Thanks for your reply. There is an automatic bleed valve on the system. Is there anywhere else I can bleed the system for the HW ciircuit?

The balancing valve? Is this the valve which is placed at the entry to the water cylinder? It was opened only a small amount and I have now oened it fully. It doesn't seem to have changed anything.

I can turn the central heating off and the underfloor and it doesn't improve. The system should definitely work in this configuration.

 

[jackthom]

Is there only one motorised valve in the system?

I'm assuming there is a 3 port valve for the underfloor heating/DHW cylinder.

When only the cylinder thermostat is calling for heat the normal arrangement is for the valve to be at the rest position and the hot water flows through port B to the cylinder.

Is that how your system is plumbed and can you feel the flow of hot water towards the cylinder and nowhere else?

 

[graham964]

No there are two. One diverts some of the flow from the central heating circuit to the underfloor heating. The other located in the airing cupboard allows the flow to go through the water cylinder.

The suspect unit for the ch and water heating is effectively a T-piece with a motorised valve bolted on it that presumably when the central heating is off should allow all the flow through the water cylinder. Is this what you call a 3 port valve?

This valve incidentally connects to the water cylinder about 1ft up the cylinder and there is a connection at the base of the cylinder which I assumed was where the heated water from the boiler goes in. The water temperature at the point 1ft higher which passes into the control valve is cooler which I assumed is correct as the heat has been transferred into the water in the cylinder.

I can't really feel a flow

Thanks for any advice

 

[jackthom]

Untitled

• jackthom
• 19 Dec 2008
• 18

If the valve is similar to this one, the bottom connector, marked on the valve base "AB", is where the hot water from the boiler enters.

The connector on the left of this picture, "B", is usually the flow to the hot water cylinder and "A" would go off toward the UF heating circuit.

When only the cylinder is calling for heat, does the boiler fire up, how long does it keep firing and where does the hot water go?

 

[graham964]

I have now done some research and I think I understand how it all works. Jackthom you have correctly identified the unit I have which is a Danfoss HSA 3 port valve. To check it I took the actuator off and rotated the spindle it was a little stiff but did rotate in both directions (should you be able to rotate it through 360deg? It was possible with mine). I sprayed it with a little wd40 and it seemed to rotate quite smoothly. I then reassembled and drained all the hot water off in the cylinder (we have an electric immersion heater which we are using at the moment) the boiler then fired up and the water flowed from the boiler via the AB port it was then all diverted in one direction into the water cylinder at the base of the tank via port B. The boiler runs for about 1minute and then turns off. It will then re ignite about 5 to 10 minutes later and run for about a minute again. Is this correct? I feel that the boiler should run for much longer.

My suspicions are that the valve may not be opening fully however I do believe that the actuator is working as when I turn on the central heating the boiler ignites and the other port gets hot and the radiators heat up. The boiler also stays on while it heats up the radiators.

The water cylinder heater tubes could be partially blocked. The cylinder is about 8 years old. Is this likely?

It could possibly be the water cylinder thermostat is giving a signal that it is at the desired temp currently set at 60degC. Not very likely I would guess.

I am not sure it could be anything else unless the controller is giving problems, it is a Potterton Suprima and I replaced the controller about a year ago. I have to say this unit has been problematic but it usually just gives the flashing red light condition on the boiler and resetting clears the problem and the water and central heating then work. It hasn't done this for a while though.

Is there anything I should do before draining down and inspecting the valve and attempting to flush the cylinder (if this is appropriate any recommendations on how to do it).

I haven't done any electrical tests so far should I do something here?


Any advice much appreciated