Hello. Last month I had a plumber install my underfloor heating system but it failed when he tried it (the base of the hot water cylinder popped out). He has not returned and I wander if anyone could explain where the problem might stem from. Diagram of system attached Basically I have a copper hot water cylinder, heating water via immersion (free electric due to wind turbine, with automatic shut off when not operating). Water goes from here to A Myson UFH thermomixing valve to circulating pump (Grundfos25 60 130 setting 3) to manifold and into heating loops (120m total length) then returns to manifold and back to mixing valve. The cool water goes towards a circulating pump (Grundfos 15 50 130 setting 1) before returning to the cylinder. A pressure vessel is located above the cylinder. The system was filled with cold water initially with the tap then closed to create a closed system. Is there an obvious flaw in the plumbing here? Is there a need for the return circulating pump between the mixing valve and the cylinder. After the cylinder popped the plumber indicated that a small water tank above the cylinder may be more appropriate than the pressure vessel!! Why did the base of the cylinder pop out? do the forces of the two pumps combine? Any help much appreciated
Underfloor heating - Cylinder popped
- Thread starter MURRAY1
- Start date
Sponsored Links
- Joined
- 10 Oct 2011
- Messages
- 16,396
- Reaction score
- 4,041
- Country
What type cylinder? , surely not a vented? 
if so is this thread a joke?
Looking at the diagram i'm guessing it is , wow.
if so is this thread a joke?Looking at the diagram i'm guessing it is , wow.
Only skim read the op. Sounds like the cylinder was an open vented heat bank. Installer has pressurised it. Stupidly. Cylinder has given up. They're not designed to be pressurised.
Installer is a dumbass.
Installer is a dumbass.
View media item 64923
I dont think your plumber is a plumber and he probably wont be back, dont whatever you do let the cylinder heat up as you will have a flood as the cylinder isint strong enough for the pressure, only thing I can suggest is to try and find someone through recommendation.
I dont think your plumber is a plumber
and he probably wont be back, dont whatever you do let the cylinder heat up as you will have a flood as the cylinder isint strong enough for the pressure, only thing I can suggest is to try and find someone through recommendation.Sponsored Links
The cylinder has a maximum pressure rating which was exceeded. The water expands when heated and if the expansion vessel was too small, the rated pressure could easily be exceeded. There should be a pressure relief valve (PRV) that would open, at a pressure below the cylinder's pressure rating, to discharge the excess water if the expansion vessel failed. There probably should also be a P&TRV as well.
I suspect your installer realized all this when he had destroyed the cylinder. An open vented system would be much safer.
Given the doubts about the installer's competence, I suggest you start by checking the pressure relief valve (piped to outside) and the high-limit cut-off thermostat. Using an electric heater on this volume of water unvented is asking for a disaster. I'm fairly sure it would be illegal, but think the G3 Building Regulations only apply to domestic hot water systems, not to heating systems.
I suspect your installer realized all this when he had destroyed the cylinder. An open vented system would be much safer.
Given the doubts about the installer's competence, I suggest you start by checking the pressure relief valve (piped to outside) and the high-limit cut-off thermostat. Using an electric heater on this volume of water unvented is asking for a disaster. I'm fairly sure it would be illegal, but think the G3 Building Regulations only apply to domestic hot water systems, not to heating systems.
- Joined
- 10 Oct 2011
- Messages
- 16,396
- Reaction score
- 4,041
- Country
Well , if it were a grade 1 then you 'would' of had a max working head of around 25 metres , my guess being it is a grade 3 with around a 10 metre head.
, my guess being it is a grade 3 with around a 10 metre head. Looking at the diagram, it would appear a satnadard cylinder is used as a heat source heated by a 3kw immersion heater. Perhaps the drawing does not show all the components.
I think your plumber must be on a fast bus to get away from Aberdeen hence he is not answering the phone
I think your plumber must be on a fast bus to get away from Aberdeen hence he is not answering the phone
Apart from the obvious (and already stated) "pressure too high for cylinder" problem, the design is wrong as well. The second pump (which you've drawn the wrong way round BTW) isn't needed - and in fact it will be "dead headed" when the UFH is up to temp.
Actually it's worse than dead headed as it's the suction side that will be shut off so the pump is more likely to suffer.
If that's all the system is, then the UFH pump will handle the flow from/to the tank. As long as the TMV calls for more heat, then some of the flow will be drawn from the top of the cylinder, and the excess return will go back to the cylinder.
Unless the UFH pump is marginal in size and/or there are some very long pipe runs - in which case it would be better to cure the problem instead of trying to cure the symptoms.
Actually it's worse than dead headed as it's the suction side that will be shut off so the pump is more likely to suffer.
If that's all the system is, then the UFH pump will handle the flow from/to the tank. As long as the TMV calls for more heat, then some of the flow will be drawn from the top of the cylinder, and the excess return will go back to the cylinder.
Unless the UFH pump is marginal in size and/or there are some very long pipe runs - in which case it would be better to cure the problem instead of trying to cure the symptoms.
I don't see who is designing this system!
A 3 kW immersion heater will give just 3 kW of power which would heat about 20-30 sq m of floor area of UFH.
Not really much heat.
That's based on 150 w/m2 which is hardly enough heat output for a draughty old property. Its likely to need 300w/m2 but that's hard to achieve practically.
That's assuming you have 3 kW continuously. You could well have that on a mountain top. But 3 kW will only heat one smaller room and not a whole house in a windy location!
So whose idea is this?
Tony
A 3 kW immersion heater will give just 3 kW of power which would heat about 20-30 sq m of floor area of UFH.
Not really much heat.
That's based on 150 w/m2 which is hardly enough heat output for a draughty old property. Its likely to need 300w/m2 but that's hard to achieve practically.
That's assuming you have 3 kW continuously. You could well have that on a mountain top. But 3 kW will only heat one smaller room and not a whole house in a windy location!
So whose idea is this?
Tony
Hello
It would appear that there are a few problems I am left with!!! To explain further- the property is an office (converted mill building) fully insulated and with a floor space of approx 36m2, as such heat requirement is low. I hope to build a house directly adjacent to the office, over the next few years and the idea was to connect the UFH of the office to the larger house system (heat source still to be decided). Currently though I need to heat the office standalone. I was looking for a temporary and relatively cost efficient solution due to its temporary nature. As electric is free but intermittent (although pretty consistent during the winter months when heat required) a form of buffer tank was suggested with 3kw immersion. As was a closed system due to no other hot water requirements in the office. it was thought a standard cylinder would do the job as a buffer tank and source for the UFH mixing valve!!
What I need to know is- Assuming the pipework is ok from and too the cylinder (apart from the pump between the mixing valve and the cylinder not being required, as Simon has indicated) what do I need in terms of a cylinder, pressure vessel, water tank etc for it to work?? Bearing in mind there is no loft for a watertank.
thanks
It would appear that there are a few problems I am left with!!! To explain further- the property is an office (converted mill building) fully insulated and with a floor space of approx 36m2, as such heat requirement is low. I hope to build a house directly adjacent to the office, over the next few years and the idea was to connect the UFH of the office to the larger house system (heat source still to be decided). Currently though I need to heat the office standalone. I was looking for a temporary and relatively cost efficient solution due to its temporary nature. As electric is free but intermittent (although pretty consistent during the winter months when heat required) a form of buffer tank was suggested with 3kw immersion. As was a closed system due to no other hot water requirements in the office. it was thought a standard cylinder would do the job as a buffer tank and source for the UFH mixing valve!!
What I need to know is- Assuming the pipework is ok from and too the cylinder (apart from the pump between the mixing valve and the cylinder not being required, as Simon has indicated) what do I need in terms of a cylinder, pressure vessel, water tank etc for it to work?? Bearing in mind there is no loft for a watertank.
thanks
Investigate whether it is legal.
The G3 Building Regulations safety requirements for an unvented hot water cylinder are quite involved, but are necessary because an overheated cylinder can burst in an explosive manner.
I don't want to dramatise this, but your arrangement could easily take your entire office down IF it were to exceed 100 degC and rupture the cylinder. This has happened with a domestic cylinder that had been rigged as an unvented system (like yours) and on which the safety devices were missing or defective (on a fishing boat, Fleur de Lys).
A large volume of water with an electric heater and few safety devices sounds very dodgy. What happens the current when the cylinder is hot?
Go on YouTube and search for "Mythbusters water heater blast".
I'll link to it when I get home.
I'll link to it when I get home.
Or http://www.waterheaterblast.com/
an unvented electrically heated cylinder on which the safety devices have been intentionally disabled.
This is interesting reading, if you're interested in that sort of thing.
http://www.maib.gov.uk/cms_resources.cfm?file=/fleur-de-lys.pdf
Nah - that ones rubbish for DIYer context.
This one is much betterer.
This one is much betterer
.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
