Heating Fine - No Hot Water

[Donbhoy]

If the Op could give a clearer explanation of what actually happens from BOTH the hot and cold taps in the bath it would be easier for us to understand what the problem is.

At one point he seemed to say he got hot water out of the cold tap after a couple of minutes!

Tony

Apologies about that, the post where i said the hot water came out of the cold tap was a typo.

The hot tap runs cold, then occasionally runs hot for a short while, eventually slowing down to a dribble and then stopping.

In other cases, the hot tap runs cold with a strong flow, then slows down to a dribble but the water is still cold.

The cold tap just runs cold all the time, thankfully!


The top pipe where the hot water should flow from is hot.

 

[Donbhoy]

A constant, strong stream of water for one or two minutes sounds like most of the contents of your cold tank. The fact that it dries up suggests that the tank fills very slowly. This is a second problem not related to the temperature.

The big question now is this: How does that tankful bypass the hot cylinder and make its way directly to your hot taps. The bit of hot at the end can, I believe, be explained thus: When the cold tank runs dry, the highest water in the system is the stuff in the hot pipework above the cylinder. This will run down, pushing warm water out of the bottom of the cylinder.

Possible answers are:

1) The entire hot water system is plumbed wrong and your hot taps are connected to the cold feed.

2) There is a pipe linking the cold feed across to the cylinder's hot outlet.

3) There is a mixer tap somewhere in the house which allows free flow of cold tank water into the hot pipes, even when it's turned off.

Point two is a possibility if your heating system is what I think it is. The clue is in the way the boiler behaves when the hot tank is full of hot water - which I think you'll find it always is. The boiler is cycling on and off on its own thermostat. This can happen if some incompetent plumber fits a motorized valve to the cylinder heating coil but doesn't bother to link it to the boiler controls. It will also happen if there is no motorized valve at all and the cylinder is allowed to reach boiler temperature. A cheap(ish) way to reduce the hot water temperature to a safer level is to bleed some cold tank water from the cold feed across to the hot pipes. The operative word here is BLEED. To make this work you need a valve that can be adjusted.

Time for more detective work. Look for anything that links the cold feed or cold tank directly across to the hot pipes.

Just one more thing: You mention a "two hour heating/water programme". Does this mean you cannot have heating on its own?

Option 1 doesnt sound very appealing!!!

I will have a look to see if I can find a link between the cold water and hot pipes.

The options i have are 'heating and water' and 'water only' so no way to have heating on only.

Thanks

 

[Donbhoy]

there might be a problem with the valve/flow switch, that operates the flow of water usually held next to the hot water cylinder tank, there shoud be a box that has a flow switch that can stop the flow of hot water into the heating or taps. Uually 3 settings, one for the radiators and one for hot water and one for both (something like that) have a look at that and put it on both

Is that a silver box, with honeywell embossed on it? If so, i do have 2 of them in and around the pipework. Any idea which setting would be for both radiators and hot water?

 

[Space cat]

Is that a silver box, with honeywell embossed on it? If so, i do have 2 of them in and around the pipework. Any idea which setting would be for both radiators and hot water?

It sounds like you have two motorized valves (zone valves) in your system. If these have been plumbed and wired correctly you should have the option of heating only, hot water only or both. They are not relevant to your current problem because you do have a cylinder full of hot water - UNLESS ONE OF THEM IS IN THE WRONG PIPE!!

There should be one in the pipes leading from the boiler to the cylinder heating coil and another in the pipes from the boiler to the radiators. There should NOT be one in any of the pipes carrying water to your taps. See if you can work out where they are. Also look for a small box strapped to the side of your cylinder with wires coming out of it. That'll be your cylinder thermostat.

 

[Donbhoy]

Is that a silver box, with honeywell embossed on it? If so, i do have 2 of them in and around the pipework. Any idea which setting would be for both radiators and hot water?

It sounds like you have two motorized valves (zone valves) in your system. If these have been plumbed and wired correctly you should have the option of heating only, hot water only or both. They are not relevant to your current problem because you do have a cylinder full of hot water - UNLESS ONE OF THEM IS IN THE WRONG PIPE!!

There should be one in the pipes leading from the boiler to the cylinder heating coil and another in the pipes from the boiler to the radiators. There should NOT be one in any of the pipes carrying water to your taps. See if you can work out where they are. Also look for a small box strapped to the side of your cylinder with wires coming out of it. That'll be your cylinder thermostat.

Hopefully your still there Space cat, got called away for a few weeks with work... unfortunately the no hot water situation hasnt resolved itself!!

I tracked the 2 motorized valves and they appear to be going to the right place.

Re. the options I have (no heating only), i am restricted by the timer I have connected to the heating system. It's a old style one, with a rotating dial where you set 2 on/off periods. The control switct attached to this can be set to either, Water only (up position), off (middle) & water and heating (down position).

I also looked at the visible pipes and I can't see any link between the hot and cold pipes.

Also, when i said i had moved into a new house, i didnt mean a new build, and it looks like the boiler/pipework has been here for a while so hopefully it's not a major problem with the plumbing having been done wrong.

Would it help If i was to host some pictures of the boiler/tank/surrounding pipework to give you a better idea of what I'm on about?

Cheers

Andrew

 

[Space cat]

A picture can save a thousand words. The important areas are the cold feed (including any side branches), the pipes coming out of the top of the tank and the pipes around the cold tank.

I'm particularly interested in any pipes coming from your cold tank. You will have a rising main feeding your ballcock, an overflow, a vent pipe hanging over the top and at least one pipe, the cold feed, leading to the bottom of your hot cylinder. Are there any others? Where do they go?

NB: That vent must NOT be under water. That's one way for cold water to get directly to your hot taps. If you follow the vent pipe downwards you should arrive at the top of your cylinder. It must be open all the way - no valves of any kind allowed - AND it must never turn upwards. That's another way of saying that from the top of the cylinder all the way to the open end it must never turn downwards, except at the very end where it hooks over the top of the tank. Imagine yourself as an air bubble once more. You're sitting in the top of the hot cylinder. Can you escape up the vent?

While you're examining the tank, see how fast it fills when you run a hot tap. If it's very slow, this will explain why your hot taps keep slowing to a dribble; the tank is empty. It's a separate problem but you might as well fix it.

 

[Donbhoy]

http://s233.photobucket.com/albums/ee39/Donbhoy1981/


ok, ive taken some photos and you should be able to see them by clicking on this link. apologies for some of the quality, it's a small space and i was having to hold a torch too!!

I ran the hot tap and watched to see re. the level of water in the cold tank. It didnt change.. not sure if that's a good or a bad thing!

If you need more specific photos of a certain area then let me know and i'll try my best.

cheers

andrew

 

[Space cat]

I ran the hot tap and watched to see re. the level of water in the cold tank. It didnt change.. not sure if that's a good or a bad thing!

I would expect the water level to drop, although you'd have to run off a few gallons to see it happen. Naturally the ballcock would open to top up the level but you would see this happen unless the valve outlet is under water - which is wrong by the way! Even then you would hear it.

When the water slows to a dribble, that's when I'd expect to see an almost empty tank up there! If the tank is still full when the water dries up, where did it come from? Hopefully not the small tank because that's the header for your boiler!

I see from the pictures that your boiler is above the cylinder and you have a tank stat on the right and what looks very much like a three port valve at the back. Other pipes from this area will lead to the small tank and to your radiators. This pipework should be completely isolated from the pipes on the left of the cylinder. Those ones should connect only to the big tank and to your hot taps. I can see a pipe coming off the top of the cylinder, turning right and then heading upwards. Hopefully it will become the pipe that hooks over the top of the cold tank but here's a question. Are there any side branches on it? There had better be for that is the only way you will ever get hot water out of that tank!

 

[Donbhoy]

I ran the hot tap and watched to see re. the level of water in the cold tank. It didnt change.. not sure if that's a good or a bad thing!

I would expect the water level to drop, although you'd have to run off a few gallons to see it happen. Naturally the ballcock would open to top up the level but you would see this happen unless the valve outlet is under water - which is wrong by the way! Even then you would hear it.

When the water slows to a dribble, that's when I'd expect to see an almost empty tank up there! If the tank is still full when the water dries up, where did it come from? Hopefully not the small tank because that's the header for your boiler!

I see from the pictures that your boiler is above the cylinder and you have a tank stat on the right and what looks very much like a three port valve at the back. Other pipes from this area will lead to the small tank and to your radiators. This pipework should be completely isolated from the pipes on the left of the cylinder. Those ones should connect only to the big tank and to your hot taps. I can see a pipe coming off the top of the cylinder, turning right and then heading upwards. Hopefully it will become the pipe that hooks over the top of the cold tank but here's a question. Are there any side branches on it? There had better be for that is the only way you will ever get hot water out of that tank!

Hi

Got home and turned on a hot water tap, let it run to it slowed to a dribble (a hot dribble mind you). Went up to check both tanks and I don't think the water level had moved, certainly they weren't empty.

The cold water tank filler does appear to be under water also.

I checked the pipe which hooks over the top of the cold tank and I can see one branch coming off of it. The branch disappears into the wall but it is warm/hot to the touch which suggests that hot water is definately travelling through it.

Any more ideas? Hopefully we're not at dead end point yet!

 

[Space cat]

Follow that pipe that comes out of the top of the tank and goes left. Is that the one that carries on through the wall? Just because it's hot that doesn't mean there's any water in it. Even if it was empty - which I'm beginning to think it is - it could be heated by steam rising up the vent from hot water in the bottom of your cylinder.

Since your hot(ish) water stops running while the cold tank is full, that means that something is blocking the flow down the cold feed. This could be a blocked or stuck valve. You said something about turning that valve to opposite lock. Anticlockwise is fully open.

The other, very common, way in which water can fail to get down an apparently open pipe is an airlock. It happens like this. Somewhere between your cold tank and the bottom of your cylinder, the cold feed turns upwards, that is downwards when looked at from the cylinder end. It doesn't take very much. A rise of one pipe thickness will do it. You now have a column of air trapped in the cold feed. There is no way out through the hot cylinder (because there's some water down there) and there's no way out past that misplaced pipe either.

What happens next is that the hot tank fills to a depth equal to that in the cold tank. The depths are now balanced on either side of the airlock. Being at different heights is irrelevant. Hot water will never reach the top of the tank. The remaining puzzle is that water is coming out of your hot taps from somewhere and it doesn't seem to be your cold tank!

The only thing I can think of is that it's coming backwards out of your cylinder through the cold feed. This would explain why it starts cold then gets hot towards the end but this scenario would require two things. Firstly there would have to be a mixer somewhere that's letting that cold feed water into your hot pipes. Secondly there would have to be a side branch off the cold feed supplying that mixer AND it would have to be low down. The bottom end of the cold feed isn't on any of the pictures. Can you follow it down from the valve and see what's there?

Two extra questions:

1) Roughly how much water do you think you get out of the hot tap before it becomes a dribble?

2) Does the amount you get increase the longer you leave the tap turned off?

 

[Donbhoy]

Yeah the pipe that comes out of the top of the tank turns left then heads straight up and into the wall.

The valve on the cold feed pipe is turned fully anti-clockwise.

The cold feed runs straight down from that valve that i posted a picture of, takes a right and goes into the hot water tank.

Now, i ran the hot tap and I got around 4.5 litres out before it slowed to a dribble, i'd say that it is normally more than this when i dont run it for a while but hard to know for sure until i was to leave it overnight and run it again.

BUT, once i had run it I went and had a look at the cold tank out of interest and I could heart that it was indeed refilling itself! But the level had only went down marginally and there was still heaps (gallons) of water in the tank.

Cheers for your help by the way, you must be getting sick of this by now!!

 

[Space cat]

Four and a half litres is a lot less than the half a tankfull I'd envisaged. (That's the difficulty of trying to solve problems from a distance.) Your pipework could hold that much.

Scenario two: When you open a hot tap you get all the cold water lying in your pipes followed by the hot bit that was in the vent above the cylinder. After that it slows to a trickle because the cold tank can't refill the cylinder any faster.

This could be a blockage in the cold feed or it could be an airlock. Look for the conditions that would create an airlock first, namely an upwards slope in the cold feed as it leaves the cold tank. Next look for a blockage in the bottom of the tank. You'll have to drain the tank for this - which won't be easy if it's blocked!

Got to go now. Time to get some work done.

 

[Agile]

If you have a powerful torch then you might be able to look through the at the outlet connection and see if there is anything blocking th outlet like fibreglass insulation, a dead mouse or anything else.

The standard cure for an air lock is to force mains water UP the hot water feed for a few minutes. Thats often done with a hose pipe from the outside or kitchen tap to a shower mixer but the hot tap MUST be turned on before the mains water.

Tony

 

[Donbhoy]

Four and a half litres is a lot less than the half a tankfull I'd envisaged. (That's the difficulty of trying to solve problems from a distance.) Your pipework could hold that much.

Scenario two: When you open a hot tap you get all the cold water lying in your pipes followed by the hot bit that was in the vent above the cylinder. After that it slows to a trickle because the cold tank can't refill the cylinder any faster.

This could be a blockage in the cold feed or it could be an airlock. Look for the conditions that would create an airlock first, namely an upwards slope in the cold feed as it leaves the cold tank. Next look for a blockage in the bottom of the tank. You'll have to drain the tank for this - which won't be easy if it's blocked!

Got to go now. Time to get some work done.

Ok, I had a look at the pipe leaving the cold tank and it does have a slight slop upward (checked with a spirit level!) for about 30cms before it heads straight down. Is this the likely cause of my problems then?

I had a look inside the cold tank and stuck my hand in (not pleasant) and checked the cold feed pipe for blockages but i couldnt feel any.

From what you've said, sounds like it may be an airlock then?

Cheers

Andrew

 

[Space cat]

Ok, I had a look at the pipe leaving the cold tank and it does have a slight slop upward (checked with a spirit level!) for about 30cms before it heads straight done. Is this the likely cause of my problems then?

If it rises by more than its own internal diameter before turning downwards you will get an airlock. There is a temporary cure for this. You connect a hot tap to a mains fed cold tap. Open the hot tap fully then, carefully, turn on the cold tap. At this point, one of two things will happen:

1) If you have a simple airlock in the cold feed, the pressure from the cold tap will blow the air up and out into the tank.

2) If you have a blocked cold fed, water will pour out of your vent pipe.

In the first case, the hot water will work afterwards. In the second case it won't and you'll have to find the blockage. Since you've checked the bottom of the tank already, the valve is now prime suspect. You could of course have an airlock AND a blockage!

PS: The water coming into your house has air dissolved in it. Very occasionally there is so much air that the water turns cloudy with microscopic air bubbles. An airlock will keep coming back! The only permanent cure is to rearrange the pipework.