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Unvented heating system - hot water problems

(25 Posts)
Lozislovely Sun 16-Dec-12 20:57:55

I live in a 12 year old 3 storey town house fitted with an unvented heating system.

Every winter for the past 3 years we've had problems with a lack of pressue and Luke warm or cold water from the hot taps (shower on top floor being the worst offender).

We've had a plumber out every year and the explanation has been a knackered actuator valve.

Well this time around we've replaced the valve yet again but we still have low pressure and cold/occasionally warm water. We've run the taps starting bottom to top but to no avail.

I'm 99% sure that it is not the boiler as the rads are fine but at a loss of where the issue might be.

Been googling possible problems but with so many varying answers I'm concerned that calling out a plumber and being stuck with an extortionate bill without the problem being ultimately fixed.

Any ideas?? TIA

PigletJohn Sun 16-Dec-12 22:54:52

do you mean you have a combi, or do you mean you have a pressurised cylinder such as a Megalfo? You haven't got any water tanks at all in the loft, have you?

Radiator heating is entirely unconnected with hot water flow from the taps.

Full a bucket at the cold tap in the kitchen, time it, and calculate how many litres per minute it delivers, and report back. Do the same at the hot and the cold taps in the bathroom.

Please actually do this, because it is essential to understanding your problem, and half a dozen people I've said it to in the last week haven't done it.

Lozislovely Mon 17-Dec-12 08:36:21

Thanks for your reply Piglet.

We have a Potterton Suprima boiler blush and the cylinder is a santon with what I believe is an expansion vessel above.

Ran the cold water tap in the kitchen and it took exactly 1 minute to deliver 10 litres.

Did hot and cold taps separately in the bathroom and each took 2 minutes 30 to deliver 10 litres.

PigletJohn Mon 17-Dec-12 08:58:21

What colour and shape are the cylinder and vessel?

Is there anything printed on either of them or on a makers plate?

Are there any tanks in the loft?

Is there a pressure gauge on the boiler or anywhere else, graduated in Bar. and what does it read?

Has the water flow ever been better?

Have the taps been changed?

PigletJohn Mon 17-Dec-12 09:05:28

P.s.- Thanks

Do you know where the stopcock(s) is (arw) and are they full on or have they been turned down for example in the hope of reducing pipe noise?

Have any plumbing or bathroom changes been made since the house was built?

Do your neighbours have similar houses with the same problem?&

Lozislovely Mon 17-Dec-12 10:08:45

The cylinder is white as is the vessel. There is a sticker on the cylinder with water pressure levels.

I can't find a pressure gauge anywhere. There are two round 'valve' type things on the pipewor to the left of the cylinder. If I turn one I can hear water rushing through but it is impossible to tell (for me anyway) what they are for.

We have one tank in the loft.

The water flow has always been temperamental.

No change to any taps at any time, they are all original.

I think the stop cock is under the sink (at work at the moment so cannot check).

Not aware if the neighbours have the same issues (house next door empty at the moment).

PigletJohn Mon 17-Dec-12 10:35:06

thanks, I think I know the sort you mean, like

I am puzzled that you have such poor water flow upstairs. Usually this sort of cylinder (similar to a Megaflo but with a separate expansion) is fed at mains pressure, and the flow and pressure are good in a modern house.

The flow at your kitchen sink cold tap is unusually poor. It is a useful guide because it is the most that you can expect to get from any tap in a pressurised system.

It is worth looking at the tank in the loft, to see if it is e.g. 18"x12"x12" in which case it wil just be a feed and expansion for the boiler, or if it is larger and fills when you run a tap, in which case it is supplying the tap water, which would be rather strange with a pressurised cylinder, but does at least give you the option to have a pump fitted.

If yours was an old house, I would suspect that it had an old, undersized incoming water main, but a fairly new house with a pressurised cylinder ought to have a large plastic incoming main, coloured blue, and at least 25mm external diameter, with a stop cock of the same size. Have a look and see if yours does. If the internal pipes, after the stopcock, are in a smaller size, typically 15mm copper, they will restrict the flow to some extent, but yours sounds unusually bad. Look for all stopcocks and service valves, including the one in the front garden and the one attached to the water meter, and verify that they are all fully open, then backed off half a turn (this prevents them seizing). If you have ball-o-fix valves these will restrict the flow unless you have the less common full-bore ones.

I am thinking of a plumbing problem, rather than a boiler problem, so if you can get a recommendation for an experienced local person to look at the pipework, he should be able to identify the problem. If any work is needed on the cylinder (unlikely because your cold flow is also poor) you will need a person with a certificate to work on pressurised cylinders, this is a qualification that some heating engineers have. A local plumber will also know if you live in an area with poor water pressure.

Nothing you have described suggests a problem with the boiler.

Do you have a water softener?

Lozislovely Mon 17-Dec-12 11:17:52

Thanks Piglet.

Yep the link you provide is the cylinder we have. Will check the tank in the loft.

We were told previously that we have small diameter copper so put the poor pressure down to that and put up with it but only getting a dribble out of the shower (when it actually delivers hot water) is driving me up the wall.

Will check the stopcocks and valves.

Have been looking online for unvented qualified engineers and think I've found one so will give him a call.

No water softener - would that make a difference?

PigletJohn Mon 17-Dec-12 11:27:06

water softeners are sometimes fitted with small-diameter pipes and connectors, which restrict flow.

Not in your case.

A plumber could run larger-bore pipes inside the house, fairly easily if done in plastic pipe which is flexible. A modern house probably has a plumbing duct running up the corner of the kitchen and bathroom. All valves and elbows in the pipe will obstruct the flow. But to know if that would cure it, you need to find if there is good flow at the internal stop-cock. If you do, you know the problem is downstream of that. If not, it might be constricted in the ground, which is more work to correct, or at the meter.

Lozislovely Mon 17-Dec-12 12:53:16

Thanks again Piglet - don't suppose you live in the Leicester area and fancy popping round to fix it do you ???smile The plumber I was going to use hasn't been answering his phone all morning and he's the only one I've found that comes recommended!

PigletJohn Mon 17-Dec-12 13:05:23

it must be winter

they're always busy.

August is a good time to have your heating done.

I live far far away grin

Lozislovely Mon 17-Dec-12 19:35:53

One more question pls grin

What is the purpose of the grundfos pump? I've noticed that this can get roasting hot and occasionally noisy - just wondered if this could be connected to the poor pressure upstairs in some way????

No hot water again tonight. brand new valve doesn't open when hot water switched on though we can force valve into open position. We did this for 30 minutes and had hot water everywhere but the top floor.

Also water seems to spurt from all taps as though its air locked but I've been told that you can't get air locks on unvented systems???!

PigletJohn Mon 17-Dec-12 19:58:25

the grundfos pump, if dark red, circulates the hot water from the boiler, to the radiators and/or the cylinder depending on the settings of the respective thermostats.

If it is ever hotter than the water pipes connected to it, then it is either jammed or dry.

If the pump is yellow it is for something different.

If the cylinder is fed from the watermain, as is usual for unvented systems, then it is practically impossible for it to get an airlock.

What does this valve look like? Is it a 3-port or a 2-port? what do you think it does?

PigletJohn Mon 17-Dec-12 20:00:41

grundfos pumps the yellow one is made of stainless steel and incredibly expensive. I left one in a house I sold a few weeks ago because I didn't have time to change it sad

PigletJohn Mon 17-Dec-12 20:01:56

sad sad sad sad sad sad

Lozislovely Mon 17-Dec-12 20:10:02

It's an ACL Drayton actuator. We have 2 which I think one is for heating and one for hot water. When I turn on the hot water and heating only the heating actuator switches to open - the hot water one stays where it is - I thought or think that these are the 'things' that deliver hot water to the rads and hot water to the cylinder???

The grundfos pump is red - I've taken off the big screw at the front before and it spurts out hot water. I did turn it up to full whack once but it sounded like the house would blow up so I turned it down until it seemed to run silently.

My husband is talking about getting a whole new system installed (he's a worst case scenario kind of man) rather than waste more money getting plumbers out who never seem to fix it and doesn't think low pressure plays a part. We've spent around £500 so far without actually getting the underlying issue of poor pressure and no hot water resolved sad

And just thinking out loud.... How easy would it be to go to a vented system????

Lozislovely Mon 17-Dec-12 20:16:52

Can't you sneak back into the old house and tell them you forgot something?? Sure they wouldn't notice their system not working for a while as you walk out with a bright yellow pump under your arm grin

PigletJohn Mon 17-Dec-12 20:17:31

quite easy, but you would need to find an older plumber to do it.

I am convinced that the source of your problem is the low water pressure, which is either due to a poor or constricted supply, possibly due to undersized or obstructed pipework; or due to an eccentric design of installation which may be using a loft tank to supply the tapwater.

An experienced plumber should be able to see what the cause is, because I think it is due to bad pipework, and correct it. A person who is only trained and experienced in fitting or repairing boilers may have no idea.

PigletJohn Mon 17-Dec-12 20:19:24


I had a dream last week, that I was in the house collecting stuff, and the new owners walked in and said "what are you doing in our house?"

In reality, I would not do such a thing.

Lozislovely Mon 17-Dec-12 20:19:54

Thanks Piglet - I'm going to show your message to the extremely un-technical husband and try and get him to see sense!!!!!!!

Lozislovely Mon 17-Dec-12 20:20:28

I'm sure you wouldn't - at least you can dream wink

PigletJohn Mon 17-Dec-12 20:29:04

sounds like they are 2-port valves. The one for the cylinder should open if the timer or override is set to HW on and the cylinder stat is cold and is calling for heat. The one for the radiators should open if the timer is set to CH on and the room stat on the wall is cold and calling for heat.

Sometimes a 3-storey house will have a stat and valve for each floor so they are "zoned" and can be controlled individually.

Lozislovely Mon 17-Dec-12 20:35:46

So could it be the cylinder stat playing up then, as even with timer on or override it won't open? Saying that we did have hot water over the summer, it just seems to be winter - but I'm thinking that as we're using hot water and heating (well trying to) that the hot water heating fails due to low pressure???

No controls on each floor that I'm aware of (we're talking cheap as chips system here!).

PigletJohn Mon 17-Dec-12 20:42:26

that could cause it to be cold. One cause might be if the wiring for the valves has been incorrectly done (FFS) to give priority to the rads. Some people set the HW timer to come on half an hour before the CH timer to get the cylinder hot.

However it would not explain the lack of water pressure, which IMO is due to incorrect piping (FFS).

Have you observed any signs of poor workmanship around the house?

Lozislovely Mon 17-Dec-12 20:47:35

No specific poor workmanship other sh@t overall build quality!!!!!!!

Will head down the route of the pressure with plumber then and see if he can shed any light.

On a side note - ever thought about setting up a premium rate number to answer all the MN queries, you'd make a killing grin

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