strange heating problems part 2

[doozer]

Thanks to those who got back to me first time round - I turned on topic watching but for some reason I didn't get notification of new messages so I didn't realise anyone had replied. Doh!

Anyway, the original message can be found here if you need a recap

we bought the house a couple of years ago the previous owners asked us if we would like a lesson on how the heating system worked but we declined as we didn't realize it was anything special. I wish now that they had told us what was involved. They did at least leave some notes tied to various pipes which gave us an idea of what to do.

I know enough to keep the system topped up with water (but thanks for the reminder because it needs doing - how often should it be checked?). A note tied to it suggests it should be filled to 1 bar so I fill it to that (+/- 0.1) when the system is cold. When it is fully hot it goes up to maybe 1.75 at most and there seems to be an emergency pressure valve set to 3 bar on top of the red cylinder. I've posted some photos of the system here

you can see the Honeywell timer box has been bodged to the wall using a standard electrical box. I think it must be held on by a piece of twisted wire or a zip tie - I have been unable to get it off the wall despite the fact it wobbles every time you touch it so I don't think it is a screw holding it on. The wobbliness is why I suspect there may be a loose connection on the back of it.

In answer to some questions raised above:

The large (1inch?) pipes running to the boiler come in the top and can get viciously hot when the heating is on so I don't think it is a lack of water.

There is certainly no header tank - the system is sealed (I believe unvented is the technical term)

I spoke to a plumber (who never showed up - grrr) on the phone when the problem first appeared. He mentioned the bubble at the top of the hot water cylinder and I have read what it says on the side of the cylinder about establishing the bubble. It sounded sufficiently difficult that I decided to leave it alone (I will try most DIY jobs but I know when to leave it to a pro). There isn't a problem with getting hot water out of the tank so I think the bubble is ok if I understand the system correctly. The tank does need cleaning though as we sometimes get a little dirty / muddy water out when we first draw water after heating but I am happy to leave that for now. I would like more information about this system - I had a look on-line but couldn't really find much. I have done work on vented systems but this is a totally different ball park.

I would be really surprised if low water pressure was totally to blame. Even when the the control box has both switches (bottom right in photo

1) flicked to off and the lights are off the boiler sometimes comes on. I am fairly convinced that the cavatating of the pump (and hence the noise) is then caused because the three way valve is set in the off position so it is pumping against the valve. When this is happening (and thankfully it's been fine for the last few days) we don't get any hot water or heating but the boiler is going 10 to the dozen.

Many thanks

[Aidan]

There are, I think, screws underneath the Honeywell box. Loosening these will allow the controller to swivelled forward away from the backplate; pull the plug first since live terminals will be exposed. You don't have to remove the screws. They are often lost by those who do remove them, which may be why it's wobbly.

Probably only one fixing screw will be holding it.

It is. Get the installation & maintenance manual from the Heatrae-Sadia website.

I do not think that the discharge pipes from the two safety valves (Expansion relief [downstream of the pressure reducing valve] and the Temperature & Pressure relief [in the cylinder]) have been done correctly.

There should be a tundish (it could be behind the cardboard label). There is a 15mm branch below the cardboard label going to the left; I suspect this is the boiler safety valve discharge. It should have a separate pipe.

Either one of the two safety valves on the unvented cylinder should be able to discharge full-bore without causing a flood. You also need to see is either of them is dripping or discharging, since this indicates a fault that needs fixing.

[doozer]

Ok, when it's a little warmer (in case I can't get the thing back together) I will have a bit of a better go at getting the Honeywell box off the wall. I noticed the screw on the underside before but was a little scared to remove it till I knew what it was doing :o). As for there being a screw missing in the backing box I don't think so as that is firmly attached to the wall. It is just the Honeywell box that wobbles but I suppose I will find out why soon enough.

Not sure what a tundish is. A quick googling seems to indicate that it is a see-through overflow check point. If it is then we don't have one (well I've certainly not seen anything that matches that description and I have had a good look). If you want more pictures I can get some.

There is a large copper pipe (22mm?) that runs down the outside wall to ground level which I assume is the safety overflow. As some point in the distant past it has has water down it but I certainly not in the last couple of years (I suspect from when the system was being installed).

There are no drips or leaks from any of the valves so I assume everything is working fine. Once in a while I have to top up the water (where does the lost water go?) but other than that the plumbing seems to work. I wouldn't be surprised if it was incorrectly installed though. The previous owners of this place were cowboy magnets.

Thanks.

Graham

Aidan wrote:

[Aidan]

When you undo the screws, the controller hinges around the 2 lugs on the top and can be removed, leaving the back-plate and connections.

That's what I meant. The controller has two screws to allow it to be fixed to a single flush-mounted backing box. You've got a double surface mounted box, so only the l.h. one of those two screws is holding the controller onto the backing box.

A funnel. It directs the discharge pipes from the 2 safety valves into one outlet. It allows you to see whether either valve is dripping. Also (this is the important bit) if the external pipe is obstructed (by physical damage, freezing, vandalism, etc) it allows the safety valves to discharge if a fault occurs. The discharge will go over the floor, but if there's no discharge then the cylinder could burst explosively.

ground level which I assume is the safety overflow.

Yes. There should be a separate discharge pipe for the boiler safety valve, with it's own tundish. You need to ensure that 22mm is adequate for the unvented hot water storage system's safety valves, when the tundish has been fitted (see the Installation & maintenance manual). Make sure the immersion heater has the proper thermostat with a secondary manual-reset thermostat. Or get someone competent & certified to do it for you. You need to get those things properly serviced annually.

[Paul Barker]

Aidan Wrote:

Yes I too am a little worried, because the quality of installatio doesn't look like it was done by a person with an unvented certificate I am also conscerned that I can't clearly see the tundish.

The item to the left with a large black knob on is your Multifunctio control valve, this has a number of duties, it prevents back flow t the water mains, filters incoming water and sets a maximum pressure. T the right of that a much smaller device usually in blue with a number on the front is your expansion valve. In Europe it is normal to allo for expansion of the water as it heats to simply eject from th expansion valve. In the water conservation conscious UK we allow fo expansion with either a bubble top or an expansion vessel, so any wate coming out of the expansion valve indicates a fualt. Deepending how an when there are different causes behind that fualt. The output pipe o this valve is called D1 and it should fall towards a visible break i the pipework where you could view the water rushing through (or jus dripping) this visible thing is called a tundish. The connection at th top right of your cylinder is called a temperature and pressure relie valve. If the user thermostat and also the overheat thermostat fai your next line of defence is the tpr valve. The discharge pipe d1 fro this should also drop to the tundish. It is OK for the two d1's to joi before the tundish. the discharge pipe after the tundish d2 has be on pipe size larger than d1, and must drop straight down 300mm before th first bend, then gradually all the way to the exit. The size of d1 an d2 depend on distances and have to be calculated. The position of th tundish should be such that you can tell what is going on, but that yo won't get scalded by any discharge, it is acceptable to put them to th side of the cylinder not right in your face, but they shouldn't b hidden behind it. Your tundish could well be behind that tag on th right.

There is a zone valve for the central heating connection to th cylinder, which is correct. This fails shut in the evnt of a power cu which is the right thing.

I won't carry on about the position of the discharge pipe and so on, i gets more involved.

The bubble in this type of cylinder naturally becomes smaller until i is ineffective, but it is very easy to reform. The instructions are o the side of the tank. In a nutshell, shut of the cold water supply switch off all forms of heating, open the nearest hot tap and hold ope manually the tpr valve until all gurgling stops, this could take som time. Then let go the tpr valve, shut the tap and turn on the wate supply. The bubble will naturally form.

IF YOU EVER SENSE ANY KIND OF DANGER you must A/ turn off all heating sources, i.e. central heating and or immersion heater/s. B/ Open a hot tap. C/ turn off the cold supply to the cylinder. Everything will settle down after that, get an expert in.

When water is under pressure the boiling point is much higher. If any part of the integrity of that vessel or directly connected controls should fail water under pressure would on changing to atmospheric pressure flash over to steam. There is enough power in that flash over from water to steam to blow your house out of the ground.

This particular cylinder is extremely safe and ruggedly constructed, all the necessary controls are designed into the fitting kit to prevent such an event occuring. But you should know it is not something to take lightly. I would recommend you have it checked by a qualified person.

[doozer]

Hmmm, I'm a little concerned now. I have taken another photograph and labelled it up with what I think each bit is. Could you take a look at it and tell me if it's correct? If it's any help this system was installed about 10 years ago. I think I have found the tundish. As a previous poster suggested it was hiding behind a piece of card. I am hanging my head in shame for missing that before :o).

If you are on a dial up this is a full size picture of about 650KB

it normal to have what we have which is basically just a cut out bit of pipe for a tundish? Surely that would cause water to flood out all over the floor rather than down the emergency vent pipe if there was a problem. As you can see there is a tiny bit of water staining around the tundish hole but it is dry now and it looks like it has been dry for a long time.

There is no water coming out what I have marked as the expansion valve. As you can see from the picture at some point it looks like water has come out of the multifunction control valve but it has looked like that since we got the house so whatever caused that crusty build up happened at least 18 months ago.

What I have marked as the D1 (Expansion Vessel) doesn't run to the tundish but it does go to the outside world.

I am pretty sure they join after the tundish.

The D2 is certainly at least one size bigger. The drop from the tundish to the D2 join is about 300mm I would guess. The drop from the top of the expansion vessel to the D2 is probably 300mm but it is in a smaller bore pipe (the drop is hidden behind the door frame on the left in the picture).

Any discharge from the tundish will come straight out at us. Brill.

I could tell which this part was. But I'm glad we have one :o)

What would be the effect of having no bubble? I haven't done anything about the bubble as the hot water system works. Wait, don't tell, me no bubble could result in a catastrophic failure :o). What I wouldn't give for a nice simple vented system right now.

What I have marked as the immersion heater I only assume is an immersion heater as we don't have a switch or anything to turn on an electric immersion heater.

As so> Aidan Wrote:

[doozer]

I know I am talking to myself but I think I have just figured out what happens if the HW tank looses it's bubble. Ever since we got the house the HW tap in the kitchen has dripped when the hot water is turned on and we get a burst of hot water the first time we turn the tap on. As it has always been like that I assumed that was how it was supposed to be but thinking about it it probably means that there is little or no bubble left to take up the expansion of the HW. Re-reading the instructions on the side of the HW tank I think I have labelled the temperature and pressure relief valve wrongly and it should be the valve directly above the tundish on the side of the HW cylinder.

Many thanks for all your help. It's really appreciated.

Graham

doozer wrote:

[Aidan]

That's it. The pictures aren't clear, so I can't guarantee that what follows is correct. The two pipes going into it are from the expansion relief valve, and the T&P relief valve (directly above the tundish). The thing you've labelled as the T&P relief valve seems to be the Pressure relief valve for the heating. The red expansion vessel is for the heating (primary) and has nothing to do with the unvented hot water storage system.

The tundish has scale on it from when one of the two valves was discharging or dripping. It was probably the Expansion relief, the T&P relief looks like the older lever type.

Yes. As mentioned previously, the D2 pipe to outside should be sized so that it will carry the water away. It will only overflow the tundish if there's a blockage in the D2 pipe. If it couldn't then overflow, the cylinder would then be subjected to excessive pressure, possibly leading to catastrophic failure.

The 'multi-function control valve' looks crusty and should be replaced. It may be a pressure reducing valve, in which case there should be a strainer upstream of it. A replacement would probably have the strainer built-in.

The pressure would rise as the water heated up. The expansion relief valve would/should open and discharge the excess water. In the UK, unvented systems are required to have a bubble or expansion vessel to prevent the waste of this water. Elsewhere, there's no provision to accomodate expansion and the water goes down the drain. IMHO, it's best to avoid operating the two safety valves unless necessary. Sometimes they won't re-seal and have to be replaced.

I can't make that out.

That could be normal, the pressure will rise and the air bubble will get compressed as the water heats up and expands. The additional pressure will be discharged when you open a hot tap.

[Paul Barker]

Cock on.

Basically the system is sound, but I'd tra> doozer wrote:-

-- Paul Barker