Heating Fine - No Hot Water

[Donbhoy]

Hi

Recently moved into a new house and although the heating works fine (if a little cold on some of the radiators) there is no hot water at all.

The boiler is a Glowworm economy plus with an immersion water tank.

When I set it to water only mode the boiler fires up for about 30 seconds then goes off, it then repeats this until i switch it off but no hot water. When set to heating and water mode the boiler works fine and the heating comes on but there in no hot water.

However, in both cases, there is a loud clanking noise coming from the immersion water tank. I took off the metallic cover to the immersion and it seems that the noise is coming from the thermostatic rod (i disconnected this and took it out and it stopped the noise).

Any advise greatly appreciated!!

 

[Space cat]

The boiler is cycling on and off because there is nowhere for the water in it to go. Some questions:

1) Does the pump run.

2) Have you tried bleeding the pipework to the cylinder heating coil.

3) What valves have you got between the boiler and the cylinder coil?

 

[Donbhoy]

Thanks for your reply.

Unfortunately im a complete novice at this at am not sure of the answers! Posting from work at the moment so can't access it at the moment either.

How do i check 1 & 2? I'll check out the valves tonight.

thanks again

 

[Space cat]

You can hear a pump running if the house is quiet. Listen for it while your heating is on. Note that just because it runs that doesn't mean it's pumping anything!

Your cylinder coil will have two large pipes going into it low down on one side of the cylinder. Follow the top one upwards and imagine that you're an air bubble. How can you get out?

 

[Donbhoy]

Ok, as i look straight on to the hat water tank I have:

2 pipes going into the bottom right
1 pipe going into the bottom left
1 pipe at the top

The 2 pipes on the right appear to be coming from the boiler and they are hot to the touch.

The pipe on the left doesnt appear to be connected to the boiler and is midly warm at the bottom but cold to the touch on the rest of the pipe.

The pipe at the top is hot to the touch.

I turned the valve to the opposite lock on the left pipe and there was some hot water but at a low pressure (eventually just driblling from the taps). However, the no hot water situation came back this morning without me doing anything.

Any more advice greatly appreciated.

edit. Oh, and i'm not sure if my pump is running or not!

 

[Space cat]

The two pipes on the right are coming from the boiler through a valve you haven't found yet. The pipe going in at bottom left is your cold feed. That's the technical term for a pipe that brings cold water from a header tank into the bottom of the cylinder. The pipe on the top is where hot water comes out of the cylinder.

The idea is that when you turn on a hot tap, the pressure from the cold tank forces cold water into the bottom of the cylinder. This in turn pushes hot water out of the top and through your tap. When you turned off that valve you stopped water from coming in at the bottom and so the hot water stopped running out of the taps.

Hot water is lighter than cold so it tends to stay at the bottom of the cylinder, gradually pushing the hot stuff up. This is where those pipes on the right come in. They connect to a coil of pipe inside the cylinder. Boiler water flows through this coil to heat the cylinder water but the two never mix.

Now here's the puzzle. The top pipe is hot. This means that you have hot water in your cylinder. The bottom pipe is warm at the bottom. It can only get warmed up by hot water at or near the bottom of the cylinder. The pipes on the right are hot. Conclusion; you have a cylinder full of hot water!

I'm now re-reading your original post. By "no hot water" do you mean that nothing comes out of the taps when you turn them on?

 

[Donbhoy]

Cheers for that, makes sense to me!

When i turn on the hot tap i only get cold water out, but i have in the past (like last night) had hot water coming out but as i said, it may flow for a few seconds but then it just slows to a dribble and then stops.

I see valves on the right hand side pipes but havent done anything with them as i assumed that as the pipes were hot, the water must be flowing through them ok.

 

[Space cat]

Any hot tap will run cold at first. There's a pipe full of cold water between the cylinder and the tap. The question is, does the tap eventually run hot or does it dry up before the hot arrives or - and this one will be a real corker - does it just keep on running cold?

Important: If your cylinder is upstairs, do this test on an upstairs tap. If the cold feed is blocked (quite possible in your case) AND the vent is blocked, you can collapse your cylinder by running a hot tap on the floor below.

 

[Donbhoy]

ok, got home and let a heating and water programme run for 2 hours, Let a bathroom tap run for ages and hey presto, hot water! But.... it stopped to a dribble after running hot for a short while. Would this fall in with your thoughts about a blocked cold feed pipe?

 

[Space cat]

Let a bathroom tap run for ages and hey presto, hot water! But.... it stopped to a dribble after running hot for a short while.

It would make sense except for one thing. Where did all the cold water come from if not down the cold feed pipe? Very roughly, how much cold water did you get out of that hot tap before it turned hot; pints or gallons? Maybe a whole cold tank's worth?

The fact that the flow sometimes reduces to a dribble does suggest a partial blockage or airlock somewhere. It's time for some detective work and you'll need access to your cold tank. Firstly, is there any water in it? Secondly, when you run that hot tap, does the ball valve open to keep the tank topped up. Thirdly, if the ball valve doesn't open, does the water level drop until the tank is nearly empty?

 

[Donbhoy]

Ok, i'll check the position with the cold water tank when i get home tomorrow.

The cold water tap ran with a constant strong stream of water for say 1-2 mins before hot water started coming out.

One thing I did notice this morning though was that although a 2 hour heating/water programme had completed, when I ran a hot tap just to check hot water would run, it didnt. It ran cold, then the flow slowed down to a dribble but the water was still cold. Is it possible that the problem is intermittant?

In any case space cat, thanks for all your help so far!

 

[Agile]

A very easy test is to feel the cylinder at the top outlet when the hot water comes from!

Is that hot?

If cold thent he cylinder is not heating.

If its hot when the water from the hot tap is cold then the pipes are crossed somewhere and the hot is not flowing out of the cylinder.

Have you had any plumbing done? Have you closed any valves?

Tony

 

[Space cat]

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?

 

[Agile]

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

 

[jezmoz]

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