Hot and cold pressure drop off Unvented system

[NeilRob]

I have an unvented system, ie both hot and cold are on mains pressure; there is no cold tank in the loft and a pressurized hot cylinder in a downstairs airing cupboard.

I have just fitted a surestop water switch as the stop cock had seized. I turned off the water in the road and had to drain the cold pipes. The water switch works fine and there was no debris in the rising main. On refilling the system I find the water pressure/flow reduces after a few seconds no matter which tap I try. Any ideas why this is?

 

[wetshoes]

Do you have a kitchen or outside tap that is fed from the "mains" - ie before the water has gone through your pressure reducing valve?

If you do, then get a bucket or kitchen jug and work out roughly how many lites per minute of water you are getting.

 

[Happyplumber]

if this problem started after you fitted the sure stop,then obviously thats what is causing the problem

Otherwise there maybe blockage in the strainer

Highly likely its the surestop or you havent turned on the stop cock fully ,,which particuliar unvented cylinder do you have ?

 

[NeilRob]

I forgot to say that I bypassed the surestop once the problem surfaced but it doesn't any difference. I have turned the stop cock in the road fully on; the one in the house is jammed and so no different to how it was before fitting the surestop.

There is no strainer, at least not on the cold nor is there a pressure reducing valve. I can't see any markings on the hot cylinder.

I will try measuring the incomming pressure and flow rate over the weekend.

The only other thing I notoced is that surestop didn't operate when first tested so I replaced it thinking it was faulty but I now see that it only works when more than one tap turned on, ie does not operate if no taps on. Perhaps there is a blockage in the rising main or the pressure is quite low so it doesn't work properly which is a bit unlikely.

Could I have disturbed the mains so that some gunge has got into the external pipework and starts to block once water starts to flow? I find it odd that pressure/flow is fine for a few seconds and then trails off.

 

[buck51]

If you have a unvented cylinder, then you will have a combination valve / pressure reducer valve, are your cold taps fed direct off the cold main or from this valve, usualy by the cylinder and it will also have a strainer in the bottom.
It is not unusual when you turn a stop tap back on to get a load of crud come through

 

[wetshoes]

What make & model of cylinder is it ?
If it's unvented it should have a reducing valve, often alongside the cylinder but it could be somewhere else.

 

[NeilRob]

Thanks for the suggestions, I am away tomorrow but will look at the cylinder for the answers to your questions on Friday. Don't know if the cold taps are off the rising main - I just assumed they were.

 

[NeilRob]

Just another thought. The rising main comes into the house via cupboard (where the jammed stop cock and surestop are located) under the stairs and pipe then goes through the ceiling.

The kitchen has been extended (not by us) so pipework there all changed from when built. Turning off road stop cock shuts off kitchen sink cold tap straight away but bath (upstairs) keeps on going for ages - all other cold taps similar to bath, ie they don't quite shut off. Does this suggest kitchen on rising main and all other cold after pressure reducing valve?

Cylinder in utility room behind kitchen and near to stairs. Cold feeds into this cupboard and there is a gate valve labelled stop cock (cold?) which I cant move. There are another gate valve labelled upstairs hot taps which do shut off when it is closed. There is another gate valve feeding the bottom of the cylinder, not sure what it does but assume it is cold into cylinder.

 

[wetshoes]

Whats the make and model of the cylinder ?
Can you post a picture ?

 

[NeilRob]

It is an Ariston Contract STI210 Indirect ProTech.

 

[wetshoes]

You should have a pressure reducing valve then (if you don't then you need one).

If you can find where it is you need to find a tap or outlet that is "before" the reducing valve, maybe a garden or kitchen cold tap and measure how many litres per minute you are getting.
Then see how many litres a minute you get from your bath hot tap and let us know.

 

[NeilRob]

Don't have an outside tap and haven't measured flow at bath as water seems to have righted itself and is back to normal. Only thing I had to do is up the pressure at the cylinder as it was down to 1.2 bar and the installer left instructions to set it at 2.5 - 3 bar; there is a gauge fitted next to the filling loop.

I did look closely at pipework around cylinder and discovered what the handbook calls a combination valve that splits water for hot and cold and connect to the expansion vessel/cylinder/overlflow. The former (labelled RWC 3.2 bar) includes a line strainer (although I don't know how to open it up) has 3 x 22mm pipe connections and the latter (labelled RWC 6 bar) includes a non-return valve has 3 x 22mm and 1 x 15mm (overflow connecting to tundish pipe off cylinder) pipe connections; one or both both seem to have a presure reducing element.

Have also discovered house seems to have 2 rising mains, one (the original) in black plastic under the stairs and the other in blue mdpe at the rear of cylinder. This would explain why hot seems to go on forever when first main is shut off. Not entirely convinced the first does anything now and will experiment to see which taps are connected to which main.

Thanks for all the suggestions as it has been an interesting journey.

 

[wetshoes]

Sounds like you've topped up the pressure in your heating circuit using the filling loop ? This won't have anything to do with pressure & flow from taps.

All the same glad to hear its sorted itself out.


regards