No Hot Water

Joined
21 Dec 2006
Messages
9
Reaction score
0
Location
Hertfordshire
Country
United Kingdom
Hello all

I am a trainee plumber, sadly without a mentor, and I have come across a problem which I can't figure out and would really appreciate some help.

My water cylinder is no longer getting heated up, so I have no domestic hot water. The water is however getting heated in the boiler and the central heating is working fine.

The problem occurred after I carried out two tasks. Firstly I replaced the radiator in the bathroom, which it turns out is connected into the H/W circuit. The pipes to it branch out from the entry and exit to the coil in the hot water cylinder.

The second task I carried out was to lower the height of the F/E cistern in the loft as it was originally installed higher than the Cold water storage cistern.

On completing the two jobs there was a whistling sound coming from the pipes and neither the central heating or hot water were working. I bled the system of air and gradually the whistling sound went away and the central heating began working again. Unfortunately the hot water is still not working.

I have since raised the F/E cistern back to where it originally was (in case lowering it caused the problem by reducing the head of water), but still there is no hot water. I have tried bleeding the system but it hasn't made any difference.


The layout of the system is as follows (oh, I live in a flat, by the way):

Boiler - Potterton Netaheat 10-16 MkII F (located in kitchen)
Has four water pipes connected up, 3 at the bottom 1 at the top.

2 of the 3 pipes at the bottom are for the C/H flow and return (pump included on the flow and is working fine). These two pipes go down under the concrete floor to the rads in each room except for the one in the bathroom.

The pipe at the top of the boiler appears to be the H/W flow. It goes up into the loft, where the F/E cistern and vent are connected to it. From there it drops down into the airing cupboard and connects into the coil in the hot water cyclinder (also branching off into the radiator in the bathroom), then back up into the loft, through an automatic air release valve, then through a pump (Grundfos UPS 15-60, which appears to be working as I can feel it vibrating ever so slightly) then returns back down into the bottom of the boiler (the third of the 3 pipes connected to the bottom of the boiler).

The system is controlled only by a 1 year old programmer (Sunvic select XL) on the boiler. There are no 2 or 3 port valves anywhere in the system (unless inside the boiler).

I think the system is mostly under negative pressure due the pump being located on the H/W return. I also get the feeling that the H/W was originally gravity circulated and the pump was added at a later date.

I've made a diagram of the circuit:
Hot%20Water%20Circuit.JPG

click the link below if you can't see the picture:
http://homepage.ntlworld.com/ec2208/index.mht

Any help would be greatly appreciated

Cheers

Chris
 
Sponsored Links
if you have no 2\3 port valves then it sounds like you have pumped heating and gravity hot water.

close the valves on the radiator (fed by the hot water circuit) and see if the cylinder heats up, if it does then you just need to slightly open the radiator valves to prevent it 'robbing' the cylinder circulators.


I am also an apprentice so take my comments with a pinch of salt ;)


EDIT: Forgot to ask...Is the radiator getting hot?
 
Hi, thanks for the reply. It does sound from my description like it would be gravity fed hot water (I think it probably was originally), but it is actually pumped. There is one pump on the C/H circuit and another seperate one on the H/W circuit, which looks to me like it was added as an after thought.

From what I can gather the Water inlet pipe into the boiler doubles as the return from the H/W circuit, but apart from that the two circuits are separate.

Oops, forgot to add, the radiator you asked about (I guess you mean the one in the bathroom that branches off from the H/W flow and return) has been disconnected from the system. I thought it best to remove it from the equation while I was working out what had gone wrong.

Cheers

Chris
 
HI,

Does the Boiler fire up on hot water only ?, the way you say it is piped up sounds like there could be an air lock, maybe behind the pump, have you tried bleeding the pump?

john
 
Sponsored Links
Hi John, thanks for the reply.

As far as I can tell the boiler is firing normally, that is, the same as it was prior to the work I did.

In order for the central heating to work, the boiler has always needed to have the hot water on as well. If I turn on just the central heating the boiler fires, but the rads never actually heat up; it's been like that ever since I moved in so I assume that's how the boiler is supposed to work.

Your suggestion of an air lock is interesting as that was where my thoughts were, given that the work I did will have let air in to the system. I haven't tried bleeding the pump, how do I go about doing that?

Cheers

Chris
 
There will be a large screw on top of the pump, unscrew it, dont worry, there will only be a small amount of water coming out & hopefully air, if you are feeling confident you can undo the nuts (22mm) either side of the pump (one at a time & not fully off the valve), this will release the air quicker if there is loads in the system

john
 
ec2208 said:
The pipe at the top of the boiler appears to be the H/W flow. It goes up into the loft, where the F/E cistern and vent are connected to it. From there it drops down into the airing cupboard and connects into the coil in the hot water cyclinder (also branching off into the radiator in the bathroom), then back up into the loft, through an automatic air release valve, then through a pump (Grundfos UPS 15-60, which appears to be working as I can feel it vibrating ever so slightly) then returns back down into the bottom of the boiler (the third of the 3 pipes connected to the bottom of the boiler).
This is a very tortuous route for a gravity circuit, although now being pumped it has more of a change of working.

Where do the cold feed and vent pipes join the circuit, and what's the height from between the base of the F&E cistern to the highest point of the DHW primary circuit?
 
<post removed because I've just seen the diagram above>
 
ec2208 said:
I also get the feeling that the H/W was originally gravity circulated and the pump was added at a later date.

Looking at the diagram, there is negative circulating head from the boiler to the hot water cylinder so I reckon it would never of worked without the pump, as Softus already mentioned.

ec2208 said:
Grundfos UPS 15-60, which appears to be working as I can feel it vibrating ever so slightly

This as the name suggest requires a minimum head of 1.5m, since you lowered the F&E maybe you ran the pump at less than this, resulting in cavitation noise and damage to the pumps bearings hence:

ec2208 said:
On completing the two jobs there was a whistling sound coming from the pipes

My gut feeling is that the pump is kaputt. How sure are you that it is working apart from it vibrating ever so slightly?

Hey don't trust me either i'm just another plumber wannabe :D
 
Hi Dukie, thanks for your thoughts, in particular regarding what may have happened to the pump after I reduced the head of water from the F&E cistern.

To answer your question, having said on my original thread that I thought the pump was still working, I am no longer sure of that. The vibration I could feel was very slight indeed, and considerably less than I felt in the other pump on the C/H circuit. I am now wondering if the vibration I could feel was the pump on it's way out.

I think you may well be right, so I'll remove the pump and give it a check over.

Cheers

Chris
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top