Boiler replacement scheme - safety

[Fredxxx]

The current boiler replacement scheme is for a like for like replacement.

In a friend's instance, the water is still heated through a gravity system, where just the Central Heating side is pumped.

As a result, apart from the inefficiencies, it can mean that hot water can attain 80degsC. I feel that perpetuating the unsafe nature of a system that would retain this gravity hot water heating system, hence scalding temperatures where there are young children around, is unacceptable.

Has anyone had any experience of this scheme?

[John Rumm]

You will find few[1] if any boilers support gravity circulation these days, so its a bit of a non issue really.

[1] I am tempted to say "none" if we are talking low water content gas fired condensors

[Dave Plowman (News)]

Eh? Thought the whole idea was to help with the fitment of a more efficient one?

It is perfectly possible to control the hot water temperature separately even with this layout. But most modern boilers will required some alterations anyway - like going to a sealed system.

[Bod]

I haven't, but you're correct about the gravity fed hot water being able to be controlled. Fitting a *tapstat* works.

[harryagain]

The new boiler is unlikely to be suitable for a gravity system. They will likely convert the gravity hot water bit to pumped.

If you are concerned about water temperature, thermostatic mixing taps can be fitted to the bath/wash hand basin.

[Bod]

That doesn't negate the possibility of a young child accidentally scalding itself.

[Dave Liquorice]

You're thinking of modern boilers...

A good old fashioned boiler with gravity HW does have a stat but that just sets the temperature of the primary, which for CH use needs to be 70+ C.

The HW is gravity so if the CH is demanding heat the HW cylinder also gets heated so can easily reach the primary temperature.

Modern low water content boilers aren't suitable for gravity HW systems. I suspect the easiest and cheapest option for the firm doing the replacement is to convert the system to fully pumped with a divertor valve and tank and room stats. Conversion to a pressurised primary would require extra work to find and disconnect the feed and expansion pipework, get a cold mains feed to the boiler location.

[John Rumm]

There are a few moder boilers round that will work on vented systems... Vaillant 400 series for example, and whatever Tim was fitting IIRC.

[John Rumm]

If you stick a blending valve on the outlet of the cylinder it does. However a new boiler will require a conversion to fully pumped operation with a cylinder stat anyway.

[Bod]

Agreed.

[dennis]

It does if you fit the correct one. They are compulsory in care homes unless you fit a whole system thermostatic mixer.

[Tony Bryer]

Or put tempering valves under the bath and/or basin

[Fredxxx]

Many thanks for your replies. My understanding is that a replacement boiler can't be fitted in isolation and the system must conform to building control, and so should have controls on hot water and heating through cylinder and room stats.

The current system has neither, but a Gas Safe registered installer is quite happy to fit a new boiler using ECO funding and run.

[Michael Chare]

Does the existing boiler not allow you to set the output water temperature?

For may years I had gravity hot water and I never had excessively hot water.

Likely you will have to install a fully pumped system anyway. In which case you can use a tank stat, and I would suggest having a programmable room stat. These days you can even get ones with web access.

[Fredxxx]

It does but depending on the setting gives hot water that is too hot and radiators that are too cold in the winter.

I am aware of this, and indeed I have fitted a couple of systems.

In this case my friend was using the boiler replacement scheme and I was more concerned over perpetuating the failings of the existing system.

[Roger Mills]

Indeed, since there's only one stat, and the same water is used for both purposes.

*However*, there is a solution without going fully pumped - and that is to convert to a C-Plan system, with a motorised valve in the HW circuit controlled by a cylinder stat. That way, the DHW can be prevented from getting too hot without compromising the CH flow temperature.

Having said that, it's not really applicable to this thread because if a replacement boiler is installed it will inevitably involve a conversion to fully pumped in order to meet current building regs.

But it's still worth considering by those with gravity HW systems who want to improve the functionality *without* replacing the boiler.

[Dave Plowman (News)]

I've seen purely mechanical devices similar to a rad stat, but with a remote sensor which fits on the tank. Dunno how good they are, though. I went for a fully pumped system when I installed it in '76, as the benefits were obvious then. Surprised there are still gravity systems around.

[Capitol]

Surely another solution is to increase the size of the radiators? My boiler temp is set to around 60C which means that you can put a hand under the hot tap without problems and have lower heat losses from the tank. However I do concede that a large hot water tank is necessary.

[chris French]

In message , "Dave Plowman (News)" writes

I only converted our gravity HW system here to pumped last year.

(been waitting until I was doing other work before I bothered to do it)

[chris French]

In message , Capitol writes

And rather more expensive (and probably disruptive) to add lots of bigger rads rather than just control the HW side of things