Headscratcher, anti scald valve?

RoundyMooney

I have a strange one, folks.

Have a mains pressurised unvented system, oil heating, solar, and immersion backup.

Now, the heating and solar are working away grand, the water in the cylinder heats away to 60 degrees as set, (there may be a swing down to the bottom, depending on how long the heat is on etc., but otherwise all is well.

The problem is, the water is tepid at the taps, or at best not hot enough for baths etc. At the antiscald valve, one side is hot as you would expect, but the other isn't. As well as this, the cold taps nearest the cylinder will run warm for a second or two before getting cold again.

I'm blaming the valve (there's a non return on the hot water feed to the cylinder, btw), but two seperate plumbers have said that both are fine. The second chap reset the pressure on the hot water expansion vessel, which improved the hot water pressure (this surprised me!), but didn't do anything for the temp. I hadn't run the oil in a couple of days prior to this, so he may have assumed that the hot water temp at the taps would have risen, but it didn't, at least not for more than a second or two once the flow starts to the tap itself.

I noticed from day one, the installation is in about a year, that the bath (on the floor above the cylinder) would start off with a good flow, but it would drop slightly within a second or two, with more or less a constant temp, but while the flow is good now, the temp isn't.

-Do mixer valves pack up? To believe these lads, they don't!

-Would a pressure vessel with too much air in impede the flow of warm water?

Thanks in advance! I'm befuddled here, and don't know what to do next, changing vessels and valves could run me into dead money in the hundreds very quickly!

Joey the lips

To my experience they rarely pack up. Mainly because once set they rarely need adjustment. Having said that hopefully most of the other plumbers on site will give good input on this.

Were you showen by the plumbers how to open the valve should you need more or less water. Usually in the summer solar produces so much hot that the mixing valve needs to be adjusted to allow more cold in.

Its kinda something i would imagine would be shown however my solar knowledge is not to advanced.

sanbrafyffe

not the most familiar with solar meself.id say the cold taps near the cylinder gettin warmer water for a couple of seconds is more than likely heat transfer.the hot and cold copper pipes are touching somewhere.seperate with lagging

sanbrafyffe

ive never hear of a non return on a hot feed to a cylinder..where is the antiscald valve.is it at the cylinder which i guess.these are just the same as thermostratic mixing valves.one side is hot and the other is cold and is mixed together to give you a preferred temperature at its outlet.you can adjust them you know.you can higher or lower the temp on the outlet side???????????????

as far as your pressure.has he the mains directly into the cylinder.there should be a non return on the mains if he does.is your mains struggling at peak times?????

is your house a big house and requires a good system to operate it.

a half inch mains might be too small

this kind of installation should be done proper.

he should have a pump fed by a cold water staorage tank near by.take the cold for the fixtures after the pump and before the cylinder and do what way you want(pipe antiscald etc)

no problems

RoundyMooney

Morning all

Joey, anti-scald is at the max-there's some level of adjustment there, because if you turn it down it goes from tepid to arctic!

sanbrafyffe wrote: »

not the most familiar with solar meself.id say the cold taps near the cylinder gettin warmer water for a couple of seconds is more than likely heat transfer.the hot and cold copper pipes are touching somewhere.seperate with lagging

All pipes are lagged, sanbra, but it is a big cylinder in a small hotpress as was, the house has been done up as they say-4 loos 3 showers one whirlpool bath. almost 2k sq. ft. now.

sanbrafyffe wrote: »

ive never hear of a non return on a hot feed to a cylinder..where is the antiscald valve.is it at the cylinder which i guess.these are just the same as thermostratic mixing valves.one side is hot and the other is cold and is mixed together to give you a preferred temperature at its outlet.you can adjust them you know.you can higher or lower the temp on the outlet side???????????????

My apologies, tis' on the mains with a pressure gauge-usually between 1.5 and 2 bar there-it's only at the top of the house where the bath is that you'd notice a bit of tail off in the pressure, but I'd live with that, it's minor.

sanbrafyffe wrote: »

as far as your pressure.has he the mains directly into the cylinder.there should be a non return on the mains if he does.is your mains struggling at peak times?????

He does, as above-the mains is generally ok, notwithstanding the above.

sanbrafyffe wrote: »

is your house a big house and requires a good system to operate it.

a half inch mains might be too small

As above, mains is 3/4 I gather.

sanbrafyffe wrote: »

this kind of installation should be done proper.

he should have a pump fed by a cold water staorage tank near by.take the cold for the fixtures after the pump and before the cylinder and do what way you want(pipe antiscald etc)

no problems

Agreed, as we know pressurised cylinders can be lethal. No pump in use. The storage tanks were removed when the attic was converted, and the new system was installed at the same time.

Could it be that there's a pressure differential between what's coming out of the tank to the antiscald, and the cold feed at the other side?

heinbloed

An anti-scalding valve (the cheap standard type) operates only within certain parameters.
It is better to use an automatic mixing valve. These give a wider range of operation (changing pressure, flow, temperature). But they cost twice or three times as much, depending on quality.

All plumbing shops store these automatic mixing valves.

Could it be that there's a pressure differential between what's coming out of the tank to the antiscald, and the cold feed at the other side?

Certainly.

Get a real plumber in.

RoundyMooney

Thanks, that makes sense.

I'd thought that the valve installed was a fairly good one, but maybe not!

The link is to a pic of it, I won't embed it here because it's probably huge, hope it makes sense.

sanbrafyffe

.ya cheap and crap quailty.get a good make of thermostatic mixer vaves.i cant think of there names but a good shop will advise you.the brittish makes are normally spot on.all that comes into your house is a half inch supply.he probably enlarged it to 3/4 inch some where...........you should really have a cold water system supply from a break tank its callled

RoundyMooney wrote: »

Thanks, that makes sense.

I'd thought that the valve installed was a fairly good one, but maybe not!

The link is to a pic of it, I won't embed it here because it's probably huge, hope it makes sense.

Joey the lips

lad just to stop a bit of madness domestic mains is half inch. it legally cannot be 3/4". the o.d on the pipe measures 3/4" because it's hydrodare heavy gauge.

heinbloed

Joey the lips wrote:

lad just to stop a bit of madness domestic mains is half inch. it legally cannot be 3/4". the o.d on the pipe measures 3/4" because it's hydrodare heavy gauge.

Why is this the case?
I'm using 3/4" and 1" for my pressurised main pipes. It gives a much better flow rate and less flow noises compared to the 1/2".
I never heard of a legal requirement concerning the max. diameter of water pipes, so I ask......

Thanks.

@the OP:

The picture shows a very crude mixing valve as far as I can see. These valves are set once and won't react to varying conditions ( changing pressures, temperatures, flow rates). But the real conditions change all the time, so the accuracy of these mixing valves is not guaranteed at all.

Joey the lips

heinbloed wrote: »

Joey the lips wrote:



Why is this the case?
I'm using 3/4" and 1" for my pressurised main pipes. It gives a much better flow rate and less flow noises compared to the 1/2".
I never heard of a legal requirement concerning the max. diameter of water pipes, so I ask......

Thanks.

.

I am in work and i cannot give you links to the legislation but following you as i do I know you know its only 1/2" up to the meter and you have no chance of getting council permission to increase it to 1" unless in the orig planning permission you planned for it when tapping into the council supply.

Would you agree that of the 250000 house built during the boom years are all 1/2" up to the meter? Prob not!

RoundyMooney

I'll check the mains size later (it runs from the kitchen sink up to the hotpress). edit: it's half inch hg, 3/4 copper after.

All that aside though, there must still be an issue, if I turn the valve hard on, the water is still tepid, there's a mix there somewhere. Else it's not shutting off the cold. Turning off the hot water gate valve (feeding the bottom of the cylinder), and the hot water flow dies away to nothing-shouldn't happen!

The markings on the valve run from min, 1-5 up to max, max being maximum warm flow obviously.

sanbrafyffe

RoundyMooney wrote: »

I'll check the mains size later (it runs from the kitchen sink up to the hotpress). edit: it's half inch hg, 3/4 copper after.

All that aside though, there must still be an issue, if I turn the valve hard on, the water is still tepid, there's a mix there somewhere. Else it's not shutting off the cold. Turning off the hot water gate valve (feeding the bottom of the cylinder), and the hot water flow dies away to nothing-shouldn't happen!

The markings on the valve run from min, 1-5 up to max, max being maximum warm flow obviously.

#
can never understand why plumber change the mains to 3/4 from half.,,,,,just totaly totaly stupid practice.if you do it like this to fill a tank up in the attic,it will fill just the same as if you ran all half the way up so why increse you cost

but there is a lot of lunatics out there:D

heinbloed

Quote:

can never understand why plumber change the mains to 3/4 from half.,,,,,just totaly totaly stupid practice.if you do it like this to fill a tank up in the attic,it will fill just the same as if you ran all half the way up so why increse you cost

but there is a lot of lunatics out there

Well, that's the lunatic's argument.

The wider the pipe diameter the less the influence of friction there is.

One of the reasons why it makes sense to me to use wider pipe diameters.

To shed some light onto the situation: Try using a small diameter straw and a wide diameter straw when emptying a glass. You apply the same energy but which straw works better? And why?

RoundyMooney

That is correct gents, but in terms of what I have, it's 1/2 inch from the road, feeding the kitchen sinks, dishwasher and fridge, direct to the hotpress via cold and gate valve to the ch loop; and via hot, non return and expansion vessel to the cylinder. It's three daughters in the hotpress only, both ways, so the argument re; flow is irrelevant.

(Despite earlier, there seems to be a non return on the hot as well-I may sketch this out if it helps; I'd like to sort this out if I could).

Look at it this way, open the half inch and wet yourself and all around you. Remember we're talking two bar here, 'tis enough.

Jedstaff

Did you check if there's filters either side of the valve. Hot might be partially blocked.

RoundyMooney

Jedstaff wrote: »

Did you check if there's filters either side of the valve. Hot might be partially blocked.

Thank you, no, there are no filters there

To reiterate again, with the hot water feed only on, the pressure is very low. The last bloke said it was down to an over charged pressure vessel, but I can't see how that would impede the flow of water!

Jedstaff

I had to take in built non return valves out of one before. It was a high pressure one on a low pressure one. Did you look inside the hot inlet?

RoundyMooney

Bumping this with apologies for not coming back sooner, I haven't checked this forum in a bit.

The problem was indeed due to a pressure differential between hot and cold feeds to the mixer, a proper valve was fitted, and the problem resolved. Happy days.

Incidentally, users of solar systems should be wary against power interruptions during the day. While this in itself doesn't pose a big problem, restoring the juice while the system retains a lot of heat can fry the pump! This happened to me, and had to be sorted by a very competent chap at the same time.