vented mains pressure hot water flow problem

[action jackson]

Evening all.

I'm a regular user of the tiling forum but have popped over here to see if someone can help me work out what the problem is with my hot water flow issue? I have already had a plumber in but he is struggling to work out the problem.

I live in a first floor flat and believe i have a mains pressure, vented hot water system with 2 x electric immersion heaters. I'm by no means an expert but i believe the system consists of a water cylinder with internal coil, a separate header tank, an expansion vessel and a thermostatic mixing valve.

The issue i have is that the hot water flow has dropped off dramatically in the last couple of weeks, making it un-useable for running a bath or having a shower. Another issue that may be related is the header tank in the cylinder is continually overflowing and running through the overflow pipe. I haven't experienced this in the last 7 yrs.

About 2 months ago i had a whirlpool bath fitted with a concealed dornbrachet mixer unit and thermostatic control for bath and shower. No problems were experienced when initially installed.

The pressure in the expansion vessel was checked on Friday and was zero psi. I have pumped up to 1 bar and so far the pressure has remained stable, although it hasn't fixed the problem.

I was advised that maybe the thermostatic mixer valve for the shower/bath could be letting mains pressure pass into the hot water circuit due to the in balance with hot and cold? Is this possible and would this cause the water level in the cylinder to rise?

I should also add that the tank was removed 3 weeks ago because i though we had a crack in the cylinder, but we couldn't find any problems with the cylinder (blanked off and filled outside with cold water for 24 hours). We now think that the leak was actually coming from the overflow pipe in the header section of the cylinder which has now been fixed.

Lastly i recall checking the header part of the cylinder a couple of years ago and noticed it was bone dry! I wasn't sure why but as everything was working i didn't worry about it. (a guy at work is ex plumber and couldn't understand why i had a header tank in the cylinder for this type of system) Now the water is brimming out the top and continually overflowing!

Any sugestions or checks to carry out would be much welcomed! :icon4:

:icon4:

 

[action jackson]

Just to add the valve for the water pipe feeding the header part of the cylinder is closed (always has been), so the raising water level in the header must be caused by the water level in the main part of the tank. There is a small internal pipe linking the two parts of the the cylinder.

 

[Gray0689]

That's a thermal Store / mains flow cylinder
Sounds like the coil has gone to be honest

 

[ryanlee]

Sounds like you have a thermal store and that the coil has gone.

 

[mikegas]

You've got a thermal store hw cylinder, if your overflow is running then you either have a split coil, ball valve isn't shutting off or the thermostat on the immersion has failed causing the cylinder to overheat, I would suspect the blending valve or split coil for the pressure issue

 

[Gray0689]

Lol like a bus answers come in 3s

 

[mikegas]

Just to add the valve for the water pipe feeding the header part of the cylinder is closed (always has been), so the raising water level in the header must be caused by the water level in the main part of the tank. There is a small internal pipe linking the two parts of the the cylinder.

Valve feeding the top part of the cylinder should be open

 

[PlumbBobBob]

it must be the coil as he said the cold feed to the ball valve is turned off, see post 2

 

[Gray0689]

How long has it been fitted Newark cylinders are 10 Year guarantee I think

 

[mikegas]

it must be the coil as he said the cold feed to the ball valve is turned off, see post 2

Yeah I was already posting after post 1

 

[action jackson]

How long has it been fitted Newark cylinders are 10 Year guarantee I think

Less than 10 years. About 8 i think. I will call the manufacturer in the morning.

 

[action jackson]

it must be the coil as he said the cold feed to the ball valve is turned off, see post 2

How do i test the coil?

 

[action jackson]

Valve feeding the top part of the cylinder should be open

will it make any difference if i open the valve?

What is the purpose of the top part of the cylinder?

 

[Best]

will it make any difference if i open the valve?

What is the purpose of the top part of the cylinder?

Top part is a expansion & feed tank for the cylinder part. The overflow is almost certain to be coming from a burst coil as others have said. That probably also explains why you have reduced hot flow.
On some thermal stores, the mains pressure was too high & split the coil.
Hopefully you will get it under warranty. IMO a stainless steel unvented cylinder is better where suitable to fit.

 

[tamz]

Since i had 10 minutes to kill while drinking my tea before i hit the sack, i did a wee drawing of basically how it works


It works like a back to front cylinder. The elements heat the cylinder (store) and when you draw water the cold runs up through the coil picking up heat and comes out and runs through the blending valve (to cool it down a bit). The top part of the cylinder is only to top up the store for evaporation. If the top part empties it means the water level in the store will drop and your hot water will not be as hot.

 

[Best]

Agree, Tamz, but top part is better described as an expansion & feed tank, as it both tops up any water loss in store via a feed pipe from base & has a vent pipe to top of it.
IMO, the overflow should never be made of plastic on these units, as when the coil fails the water is hot running from o/flow, which could mean the fittings coming apart.

 

[stani]

Less than 10 years. About 8 i think. I will call the manufacturer in the morning.

It was manufactured. 10thjune2005

 

[action jackson]

Top part is a expansion & feed tank for the cylinder part. The overflow is almost certain to be coming from a burst coil as others have said. That probably also explains why you have reduced hot flow.
On some thermal stores, the mains pressure was too high & split the coil.
Hopefully you will get it under warranty. IMO a stainless steel unvented cylinder is better where suitable to fit.

Thanks for all the replies. The manufacturer has stated the cylinder only has a 2 year warranty. A new identical cylinder is £1,000!

Can the coil be repaired?

 

[Mike Jackson]

The coil can't be repaired. I'd look at ditching it and fitting a stainless steel unvented in place of it.

 

[Gray0689]

The coil can't be repaired. I'd look at ditching it and fitting a stainless steel unvented in place of it.

Agree cant really see why they installed a thermal store what is heating it apart from the emersion heaters

 

[action jackson]

Agree cant really see why they installed a thermal store what is heating it apart from the emersion heaters

Emersion heaters only.

Can someone please point me in the right direction for a cheap replacement? Funds are very tight at the moment.

Thanks

 

[tamz]

These are about the cheapest replacement you will get.
170 litre Direct S/S unvented Cylinder Mr Central Heating.co.uk, The Ultimate Deals in Central Heating [GOLD170D] - £400.00 : Central heating, boilers, combi boilers, radiators and plumbing supplies from Mr Central Heating

You need a registered unvented installer to fit it.

You will get around £70 for the old one from a scrappie.

 

[Gray0689]

A smallish unvented direct cylinder would suit bettering sure knen

 

[Best]

Agree with what others have said, get a s.steel unvented unit, as it is cheaper & better in every way. Great flow of hot water if mains up to it. 25yr warranty usually also. The thermal store in your case, only advantages was that it didnt require unvented regs or a copper discharge pipe to a safe point.
Don't try to save on install, - have it done properly by qualified person for safety & warranty.

 

[action jackson]

Agree with what others have said, get a s.steel unvented unit, as it is cheaper & better in every way. Great flow of hot water if mains up to it. 25yr warranty usually also. The thermal store in your case, only advantages was that it didnt require unvented regs or a copper discharge pipe to a safe point.
Don't try to save on install, - have it done properly by qualified person for safety & warranty.

What is the minimum mains pressure for uvented systems? Mains pressure is not fantastic.

Ref copper discharge pipe to a safe point, what is required for an unvented install?

I live in a first floor flat and have no access to the outside etc.

 

[ecowarm]

That is the reason you have a thermal store.
That one is made by newark copper cylinders go direct them

Andrew - 01636 678 437Mike - 01636 671 074Mark - 01636 671 072Tom - 01636 678 505
Give them the details off the label and have one made exacly the same, straight swop, easy

 

[Gray0689]

That is the reason you have a thermal store.
That one is made by newark copper cylinders go direct them

Andrew - 01636 678 437Mike - 01636 671 074Mark - 01636 671 072Tom - 01636 678 505
Give them the details off the label and have one made exacly the same, straight swop, easy

Agree
But I'd be guessing there is no prv fitted that's why coil gone so soon

 

[ecowarm]

Proberbly none or not enough inhibitor in the store

 

[action jackson]

That is the reason you have a thermal store.
That one is made by newark copper cylinders go direct them

Andrew - 01636 678 437Mike - 01636 671 074Mark - 01636 671 072Tom - 01636 678 505
Give them the details off the label and have one made exacly the same, straight swop, easy

Agreed this is the easy route but at a cost. Best part of £1,000 for the cylinder and delivery. I'm not in a position to pay this much i'm afraid.

 

[Gray0689]

It's realy your only option if you can't get at an outside wall
Is your hot press near a soil pipe?

 

[ecowarm]

Agreed this is the easy route but at a cost. Best part of £1,000 for the cylinder and delivery. I'm not in a position to pay this much i'm afraid.

Google " Discount copper cylinders" in Manchester you may get the same thing cheaper there.

 

[MattWeth]

You can discharge an unvented cylinders' relief's into a soil pipe via a HepVo waterless trap (assuming as Gray0689 says, your cylinder is located near a soil pipe so you can route the discharge line with the correct fall).

 

[mikegas]

What is the minimum mains pressure for uvented systems? Mains pressure is not fantastic.

Ref copper discharge pipe to a safe point, what is required for an unvented install?

I live in a first floor flat and have no access to the outside etc.

1.5 bar and 20lpm min

 

[action jackson]

You can discharge an unvented cylinders' relief's into a soil pipe via a HepVo waterless trap (assuming as Gray0689 says, your cylinder is located near a soil pipe so you can route the discharge line with the correct fall).

I have decided i would like to go for a 170L direct UV gold cylinder from MR Central Heating. Before i do, can someone please advise if its possible to provide a suitable discharge as per the picture below of my current setup?

 

[MattWeth]

A discharge similar to your picture may be possible. There are several things to consider though (materials / pipe layout and arrangement etc) which really need the input of a plumber / heating engineer who is qualified on unvented hot water systems. However this type of discharge is not a preferred option and needs the explicit approval of your council building control department (there's no reason to suppose it wont be granted, but they must be consulted for approval).