Central Heating goes cold downstairs when hot water put on..

[mikeluxy]

Hi There

I wonder if anyone can help on this rather irritating problem.

We have an open vented system and had the Boiler replaced just over 2 years ago....we also had a complete system flush at the same time.

We have a problem whereby if we have the hot water turned off (via the control panel) all the radiaitors are fine and all get nice and hot....up and downstairs.

As soon as we turn on the hot water the radiators downstairs suddenly start to get cold...a right pain in the arm!!

The radiators upstairs seem to stay hot but the downstairs go cold.

I have been reading online that it may possibly be the Zone Valve or maybe the Pump...?

Any ideas and suggestions much appreciated.

Cheers

Mike

 

[45yearsagasman]

It may well be the pump,but do you have a balancing valve on the cylinder flow or return?

 

[mikeluxy]

Thanks for your help.....Im afraid im not too sure on that one...can you let me know where this valve is located on the tank....?...would it be on the top or the side...?...also does it look just like a normal stopcock..?

Do you think this valve may be jammed perhaps....?

 

[45yearsagasman]

This valve may be fitted low down on the return pipe and may be a gate valve. A pic of your cylinder install would help.It may be that this valve is open too much and the cylinder is accepting too much heated water and starving the rads during a hw/ch operation.If you find the valve,close it and then open up 2 full turns to start with.It will normally be 22mm.

 

[mikeluxy]

Hi THere

I have taken 2 pix and uploaded here

//www.diynot.com/network/mikeluxy/albums/6979/27707

There seems to be no valves going into the tank that I can find....

 

[45yearsagasman]

Just had a look at your pics and I agree that there appears to be no balancing valve.I would suggest starting at the pump and removing it to check for restrictions and also removing the 3 port valve to check that the ball has not swelled.This is DIYable but not if you are not confident on drain downs and refills.

 

[spraggo]

Hi Mike
It is a possibility that the three way valve is wired to give hot water priority, meaning that the 3 port valve will only switch to central heating once the water temperature is up to heat which would be sensed by the cylinder stat. Try turning the cylinder stat down and see if there is any improvement.

spraggo

 

[45yearsagasman]

Spraggo that may well cause the symptoms but looking at the pics I think the valve is a mid pos, and the 1st floor rads still stay hot.The cable to the valve is larger than priority valves.In any case the OP states that the heating works well on heat only

 

[MANDATE]

With both HW and CH selected, it's a situation that may be misunderstood.
If both sides are in demand then both sides share the water, but this situation only lasts until one side becomes satisfied and results in the other side getting all the water.
The CH side loses heat through radiators far quicker than the HW side, so the valve will spend the most time at the CH position and dropping back to mid position occasionally for short periods (unless you run a bath)
From what you say you have no problem with CH only and no problem with HW only.
I feel 45yearsagasman was on the right track, I think it's a balancing issue.
The resistance in the CH side does not match that in the HW side.
Water will take the easiest path so the CH side gets starved.
I think if you opened all the lockshield valves a fraction more it would help balance the two sides.
Again if there is a large difference between upstairs and downstairs, I would again think they may be on separate circuits with one circuit having more resistance than the other. or even on the same circuit some radiators may need adjusting.
I agree that even with everything balanced correctly a pump can be faulty.
I removed a friends pump which was working, to find the inlet and outlet holes reduced to about 6 or 7mm which was one of the causes why a radiator was starved.

 

[spraggo]

Hi 45yearsagasman

I see your point, but there is no way of telling, by the pic, whether this valve is a three way midi valve or a thre way zone valve.

Regards

spraggo

 

[45yearsagasman]

Hi 45yearsagasman

I see your point, but there is no way of telling, by the pic, whether this valve is a three way midi valve or a thre way zone valve.

Regards

spraggo

Cable diameter. A priority valve as I remember has only LNE and not 5 wires.

 

[spraggo]

Cable diameter. A priority valve as I remember has only LNE and not 5 wires.[/quote]

Beg to differ, the Honeywell V4043H has 5 wires as used in the "W" plan.

 

[45yearsagasman]

Spraggo,sorry yeah you're right,forgot about that one,but I still think its a balance problem.Pity the OP doesn't come back.

 

[spraggo]

Hi 45yearsagasman.
apologies accepted, I would like to add that I am a 75 year old retired,
after running my own business for 50 years. So I don`t always get it right, the old memory plays me up sometimes.

Regards

spraggo

 

[ajrobb]

One problem you might get is that the boiler output is not hot enough to satisfy the cylinder thermostat. The hot water legally has to be heated above 60°C to kill legionella bacteria. It is a problem with condensing boilers - to get maximum efficiency they should be run cooler than the hot water. Some boilers allow different feed temperatures for hot water and central heating.