Unvented Hot Water Cylinder Problems & Cures

Welcome to our unvented hot water cylinder problems & cures, are you finding your getting a problem with your unvented hot water heating but don’t know what to do, well you have come to the right place, first of all we are going to give you a little history about the unvented hot water cylinder, then we are going to bring up all the common questions that we get asked but also answer most of them on this page.

The unvented hot water cylinder was invented by a british civil engineer called Thomas Hawksley in 1861 from Arnold in Nottinghamshire. He was born on 12th July 1807 and died 15th September 1893 aged 86.

In 1985 to 1986 the building regulations and the water bylaws were passed and then the unvented hot water cylinder was then allowed in the uk.

This was not the start of the unvented revolution as it was aloud in the USA, Europe and Australia 50 years before the UK.

For engineers working with these cylinders, it is good to know that in the next 10 to 20-years, it is predicted there will be twice as many unvented cylinders about.

23 Questions about the unvented hot water cylinder

Are unvented hot water cylinders dangerous to work on?
Why am I getting no hot water from my unvented hot water cylinder?
Why am I getting no water at all as I have an unvented hot water cylinder?
My water is too hot on my unvented cylinder, why is this?
There is water dripping from the plastic pipe, do I have a problem?
I can see water pouring through my pipe of my unvented hot water cylinder, what can I do?
Do I have to get my unvented cylinder serviced ever 12-months?
What does the expansion vessel do on the unvented hot water cylinder?
Im not getting enough water through from my tap and I have an unvented cylinder?
What is the Tundish for on the cylinder?
Who do I call if I have a problem with my unvented hot water cylinder?
What should I do if my unvented boiler isn’t being used?
I have poor water pressure, can I have an unvented cylinder?
Which is the best cylinder to have, a vented or an unvented hot water cylinder?
Why are there so many different pipes on the unvented cylinder?
What should the pressure be on the unvented cylinder?
How do I become an unvented boiler fitter?
My water isn’t heating up on my unvented boiler, what is the problem?
Why is my unvented cylinder leaking?
Why has my unvented cylinder exploded?
What should the temperature be on the immersion heater of my unvented hot water cylinder?
Does an unvented cylinder need a system boiler to heat up or can this be done via the cylinder?
How would I know if the plumber is qualified to work on unvented hot water cylinders?

Are unvented hot water cylinders dangerous to work on

As being an experience emergency plumber for the last 20 plus years, when coming across the unvented hot water cylinder, it has always been scary apart from when I was in my teens and felt a bit like Batman, however this is a warning to those who feel they can try and fix there unvented hot water cylinder problems. It’s not worth it! First you have to be qualified and hold an unvented certificate for these types of boilers. It can hold a big fine and possibly a jail sentence. Here is an example: last year, a plumber went out to an unvented boiler unqualified as there was water dripping via the Tundish. Later on that day, the unvented cylinder exploded causing the death of six occupants.

Why am I getting no hot water from my unvented hot water cylinder

If your not getting any hot water from your unvented hot water cylinder, then this is most likely going to be due to the immersion heater that is faulty, you may need the complete immersion heater replacing or just a stat. If you have an economy 7, diagnosing it can be very tricky, however this can be done by using separate power sauce and must be done by using a qualified engineer. Always ask if the engineer has an extension lead and a plug.

Why am I getting no water at all as I have an unvented hot water cylinder

If your getting no cold or hot water at all via the hot water tap, then this will most likely be due to the filter known as this mesh being blocked up.

My water is too hot on my unvented cylinder, why is this

If you have water that is getting too hot, it may be because the stat is set too high instead of 60 to 65° or the stat has become faulty and needs replacing.

There is water dripping from the plastic pipe, do I have a problem

If you have water dripping from the D1 to D2 pipe via the Tundish which is the overflow pipe the runs from the unvented cylinder to the water waste and to the outside. Then you have a problem, in most cases, illegal fitters tend to think it’s the PRV at fault but it isn’t. Im unable to tell you what the fault is because I am then encouraging you to do the work yourself illegally. However this can result in a couple of hours work and the cost in materials up to £200.

I can see water pouring through my pipe of my unvented hot water cylinder, what can I do

If you see water coming through the Tundish of the plastic overflow pipe, then the first thing to do is to turn the electric off to it and then the mains water afterwards. Do not attempt to fix it yourself and call a qualified unvented fitter specialist.

Do I have to get my unvented cylinder serviced ever 12-months

You don’t have to get your unvented cylinder serviced every 12-months, however if you ask should you get the unvented cylinder every 12-months then the answer to this is yes. If you don’t get the unvented cylinder serviced then the warrantee to the unvented hot water cylinder may be void.

What does the expansion vessel do on the unvented hot water cylinder

The expansion vessel on the unvented cylinder has the ability to hold water in it and expand. If your wondering what is in the expansion vessel then you will be looking at part water part Nitrogen enriched air. The hotter the water the more pressure in the vessel. When the unvented engineer checked the vessel upon a service, he/she will use a tool that finds out the pressure. By using the tool, the engineer can also find out if the vessel has collapsed or not.

Im not getting enough water through from my tap and I have an unvented cylinder

If your not getting enough water or no water at all, then either that mains water stopcock has been isolated or the filter is blocked. Unfortunately you be unable to do nothing apart from call an unvented fitting specialist.

What is the Tundish for on the cylinder

The Tundish was designed for the customer to visually see water leaking via the overflow and to call an unvented hot water cylinder specialist.

Who do I call if I have a problem with my unvented hot water cylinder

If you have a problem with you unvented hot water cylinder but unsure who to call, then please feel free to call us and we will get you a qualified unvented emergency plumber out immediately or within a reasonable time depending on where you are located. Please call us on 07720247247

What should I do if my unvented boiler isn’t being used

If your unvented boiler isn’t being used then this is fine, however, if it has not been used for 40-days or more, you will then need it cleaning/disinfecting. The simple way to do this is, if you have an indirect unvented hot water cylinder, you can turn the heat on the central heating boiler to 70° which then will kill the Bacteria in the water, it is always good to bear in mind that if you have hard water and there is a chance of scale within the unvented hot water cylinder, then Bacteria can be trapped leading to legionnaires decease. To clear the scale within the unvented cylinder, you will need to call a specialist of whom will place the chemicals inside to get rid of the scale. Once the bacteria has been killed when heating up the cylinder, you will need to run the hot water off for example, if you have 125-litre tank, you will need to run 125-litres or more of water until it is then classified as clear.

I have poor water pressure, can I have an unvented cylinder

If you have poor water pressure, then you will be unable to have an unvented cylinder unless you can find means of a way of getting better water pressure. To find out if you have good enough water pressure and flow, you will need a Weir gauge and a pressure gauge. To have an Unvented hot water cylinder you will need at least 1.5-bar water pressure and not less than 20-litres per minute.

Which is the best cylinder to have, a vented or an unvented hot water cylinder

Having the best central heating system or hot water system can be a matter of opinion, which means that one type of system might not be satisfactory for one but satisfactory for the other. With a vented cylinder, you rely on the water being gravity fed from within the property, where with an unvented cylinder, you are relying on the water pressure from the mains water pressure and flow.

Why are there so many different pipes on the unvented cylinder

The reason for the extra pipes on an unvented hot water cylinder is because there is so much more going on, having an unvented hot water cylinder can be very dangerous if not fitted with the safety pipe. You still get the flow and return on a system boiler and you will still get the hot water feed and outlet into the direct/indirect cylinder. Depending on the locating of the expansion vessel, you may find an extra pipe, you will also find overflow pipe (discharge) known in professional terms as the D1 and the D2 discharge. The D1 is the first pipe coming from the safety device followed by the Tundish, after the Tundish is the D2 water that takes the water to where it can exit.

What should the pressure be on the unvented cylinder

As explained in the paragraph above ‘I have poor water pressure can I have an unvented cylinder‘, the water pressure should be at least 1.5 where the mains water pressure should be a minimum of 3.0-bar but ideally 3.5-bar.

How do I become an unvented boiler fitter

To become an unvented cylinder specialist, you firstly need the qualification G3 which you can gain from going to a 1-day cause and exam all in one. You will need to have minimum qualifications of NVQ level 2 in plumbing or prove that you are a gas engineer.There are also similar qualification but these are the main ones.

My water isn’t heating up on my unvented boiler, what is the problem

If your water isn’t heating up and you have an unvented cylinder, you will need to call a qualified competent engineer qualified on unvented cylinders and the most likely outcome to the unvented boiler not heating up is the immersion heater or the stat.

Why is my unvented cylinder leaking

There are a few reasons why an unvented hot water cylinder can be leaking but one of the main reasons would be is because the boiler has over pressurised. In most cases as an emergency plumber Martin Smith is, the water tends to come through the overflow and out of the Tundish. It has also been known that some unvented hot water cylinders have a week spot and when under great pressure, the cylinder has popped causing a massive water leak.

Why has my unvented cylinder exploded

Like in the paragraph above ‘why has my unvented cylinder leaking‘. Explosions can be caused by a week spots but the word explosion can also be an expression for just water surrounding the unvented hot water boiler. If your looking for a real explosion, then this can be caused by having no safety devices and the cylinder that constantly heats up without switching off. This can happen when and if you use an un-qualified unvented hot water cylinder specialist. Please read the first article as an example to ‘Are unvented hot water cylinders dangerous to work on‘.

What should the temperature be on the immersion heater of my unvented hot water cylinder

The temperature is normally manufacture set at 60 to 65° and shouldn’t be any more unless maintenance work is being done by a qualified engineer. If the temperature was to rise, then there would be a safety device that would stop the water from getting too hot such as the high efficiency stat that will cut of the power to the cylinder if then it gets way too hot.

Does an unvented cylinder need a system boiler to heat up or can this be done via the direct cylinder

An unvented hot water cylinder doesn’t require a system boiler but only because it can rely on electricity to heat up the water via the immersion heaters. Having a system boiler only makes it cheaper to heat up your unvented hot water cylinder by using gas and electric.

How would I know if the plumber is qualified to work on unvented hot water cylinders

To know if the emergency plumber is ok to work on the unvented hot water cylinder, he/she should carry an ID, to show the customer that they are qualified and have there G3 markings. Alternatively they can carry an additional card for example, the gas safe card and have the qualifications printed on there. It is also wise to check the date of the qualification as there ID will only cover them for 5-years and then the emergency plumber would have to take there exam again.

If you are qualified to work on unvented cylinders and would like to join our network, then please feel free to join us on our plumbing register.

Similar to this article is hot water cylinder problems & cures.

New information update on 20th April 2016 below (Please also note after further education, we will be doing a video in the coming months all about the unvented cylinder)

CMS Approved Engineer Information below

Firstly, over 90% of breakdowns reported to us, that we attend within the first 12 months of installation, are caused by installer error or an incomplete commissioning procedure legally required by Benchmark and the Hot Water association performed by the installing engineer.

It is the legal duty of the installer engineer to inform the end user of this requirement as stated by Benchmark. 12 month service intervals are required on all unvented cylinders to validate the guarantee.

The refurbishment is a product that we are most proud of. If a cylinder has not been serviced this will place the guarantee in a null and void status. An onsite refurbishment by a CMS Approved engineer will resurrect the lifetime guarantee and point out any installation defects that need addressing, CMS will automatically contact the end user to remind them that the annual service is due, then we’ll send out a CMS Approved engineer to service the cylinder. (Please note that the cylinder in the picture has not been serviced correctly).

Finally we run training courses and we openly invite you to take advantage of these, so that you can become a CMS Approved engineer backed by the manufacturer and promote your business in the same light adding credibility to your experience.

Unvented Hot Water Cylinder