Should I get opentherm concidering the risks?

16 Apr 2008
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United Kingdom
I am thinking about my next boiler, which will be an Ideal Vogue 32c Max and maybe Opentherm via Halo and whether I should get the Opentherm option and would it save any money and possibly cause a leak in my pressurised piping that has issues?

At the moment my dumb thermostat on a Worcester Greenstar meets my needs. If has 6 time zones 6:30-8:30 19.5C, 08:30-13:00 17C, 13:00-15:30 17C, 15:30-22.00 19:5C, 22:00-06:00 15C.

My well insulated house on cold days doesn't hit 19.5C in the first period but that doesn't bother me as we are moving around. This is no doubt due to the fact that the boiler operates the CH at only 55C with around a 12C drop across each radiator so I consider the Worcester to be permanently condensing. On occasions we do override the daytime temperature by manually increasing the thermostats temperature.

Now the issue. Maybe 10 years ago we had a leak in the central heating system, which could not be found. It was cured with a bottle of rad seal that has fixed the problem. This resulted in me keeping the pressure gauge to a fraction under 1 bar cold so at 55C I get 1.5bar.

I understand Opentherm ignores the boiler controls so could pump out a lot of heat at 6:30 so not only increasing the boiler to a non condensing temperature but possibly increasing the pressure so it pops my rad seal in some hidden pipe.

Have I lost the plot? Will I save any money on gas costs? Will I threaten my rad seal?

Also, while I am thinking about it, with Opentherm does it turn the heating on early to get to 19.5C for 6:30?

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Opentherm is just a comms interconnection standard allowing controllers to be more subtle with boiler control rather than on/off. As far as I know, the controller actively sets the output power of the boiler (the modulation level) rather than the operating temperature.
If your posh new controller has optimisation built in then yes to achieve setpoint in the morning it's likely the boiler will be running at a higher power level (not temperature) to hit setpoint. And turning on early to hit setpoint- yes it does if it needs to. I have the Drayton stuff (WiFi rad valves all over the place), the box looks at outside temp, looks at room temp, looks at target room temp and fires up early enough to deliver enough energy to be somewhere near setpoint at set time. Mine is still learning the house but it's pretty good...
Just add another vessel..the larger you go the less the pressure increase when the rads are hot.
If the new boiler is installed in compliance with the manual and regs the system will need cleaning so there's always a chance your leak will return.
What Worcester model and age?
In my mothers house I found it was the TRV which caused the delay heating home, not the boiler, as with your set up I also had timed reheating after an over night switch off. Mother would be taken for a shower when carers arrived in morning so re-heat was important.

Set to 20°C at 7 am the living room would stabilise at 11 am, set to 22°C at 7 am and 20°C at 8 am and the room was warm at 8 am.

The Worcester Bosch boiler had nothing to tell one what its output was, as the user I had no idea if modulated or not, since cheating and setting to 22°C it reached temperature faster clearly it was modulated before I did that. The wall thermostat was set higher than the TRV in the hall so only on warm days did the thermostat turn off the boiler, the boiler was allowed to modulate this also resulted in hot water being available for the TRV to regulate room temperature.

I found the lock shield valves had been left wide open by the installers, and it took some time to fine tune them, having the lock shield on the supply side and TRV on return did not help either, however it did work, once set each room as at temperature required when required.

Intention had been to fit Nest, but it seemed to work spot on anyway, so never bothered.

As to OpenTherm, I can see the boiler would be better controlled, but likely it would need a link between TRV and wall thermostat, so the cost gets silly. Today I use oil so OpenTherm not an option, but to have linked TRV's will insure the boiler runs when required, £15 for non linked and £40 for linked does not seem much, until I think I have nine rooms with electronic heads, so £225 extra to have linked TRV heads. And really I have a further four rooms which need TRV heads swapping to electronic.

The old TRV's seem to have a larger thread on the heads, my electronic heads come with 28 mm and 30 mm, but it seems the remaining four are larger, so also need to swap bases, this is why as yet not done.

So if we consider non OpenTherm and OpenTherm we are likely looking at a fair amount extra, bills have risen, but less than £400 for a tank full of oil which will last the winter, and this is a large house, how many years to break even? If bill was £400 and OpenTherm dropped it to £350 then is it really worth all the effort?
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The exiting boiler is a Worcester Greenstar 42CDI. It was installed on May 1st 2008 so will be 14 years old in the Spring. Through these forums I have learnt it is over powered for my cold tap flow rate which is 12 litres a minute. The planned boiler has a DHW flow rate of 13.1 per litre. The existing boiler has a Worcester service contract so I will keep it running until it is unrepairable but I like to plan ahead so I can order straight away and know what I want. So far it has never gone wrong.

As for the cause of the leak and with no evidence I suspected when hardboard was laid over the existing bathroom floor for tiling a nail went through the pipe. This happened maybe 12 years ago. As the nail started to rust maybe 2 years later a leak occurred. As the system is now well dossed with inhibitor I think the nail stopped rusting but this is pure speculation.

So what does CH output actually mean? The Ideal Vouge 32 is rated at 26Kw while I have calculated my rads output as 12Kw. oldbutnotdated states the boiler could operate at a higher power output, which does not relate to a higher temperature. Does this mean the radiators could run cooler, as the boiler is pumping out more CH water or just that the boiler could run twice as many radiators.

I doubt the leak is be a nail.
Expansion / contraction would have pulled the repair long ago.
I would be getting prepared to have to find it and do a proper repair when you put in a new boiler regardless.

I would be looking at why your system can't do its job properly. You've a big boiler so either the controls/configuration isn't right or you live in a barn.

I would then do a system review before buying anything. Look to the modern way of heating controls (full rad control with wifi/App controls) and work backwards from what you want to get a system you will like.
Most new heating contols (Wiser, etc) seem to have opentherm or other compensation technology built in, so it's plug and play really.
Once you specify your job properly, you may find opentherm isn't needed.
When you look at Combi boilers there are several output numbers- the biggest one is for dhw, then there's output into radiators, then there are the modulated outputs (levels lower than full power so the boiler can, for example, tick over at 20% to meet demand rather than running flat out for 5 mins then off for 20 mins.
The headline boiler efficiency number is usually at full power, you have to look harder for efficiency at lower outputs. If your max heating demand is 12kw and you're not planning to extend the house any time soon you should be looking at about 15kw heat output- this may, of course, compromise your dhw needs so bear that in mind
My 3 story house has a 20 kW oil boiler, so if the energy can't be dissipated in the radiators the boiler cycles, I know I have a fault, as boiler rarely runs for longer than ½ hour before starting to cycle. However if the boiler was a modulating type, I may have been unaware there is a fault.

Don't want to mess up your thread with my problem, but seems likely if not warming the home you also have some thing wrong.

I know in parents house a floor board screw did go through a central heating pipe, we estimate it took 5 years before the leak was seen, due to where it was and last time boards lifted, but when it did start leaking is was rather a lot, that system had header tank so no limit to water leaked.

Son had boiler swapped in my old house, and did not renew the lock shield valves, and the old ones would not take pressure of new sealed system. In the winter the leaks were not really noticed, just a little loss in pressure, in summer when water cold, got wet under radiators.
I would suggest you all keep googling and find out what open therm is and actually does
I would suggest you all keep googling and find out what open therm is and actually does
Tried that- I wanted to find out if my controller is actually emitting Opentherm data or just closing the circuit...yes I can spank a chunk of cash on a pc interface for the boiler which will tell me what it's up to but I'd rather not ....
Tried that- I wanted to find out if my controller is actually emitting Opentherm data or just closing the circuit...yes I can spank a chunk of cash on a pc interface for the boiler which will tell me what it's up to but I'd rather not ....
I am in no way whatsoever a fan of OT, if someone wants to use it then of course that is their choice, but dont praise that it is some kind of fantastic answer to fuel usage, it is not, it is simply an algorythm, that may or may not work for your needs
OpenTherm is a two-way data connection between controller and boiler. Fitting it cannot increase your chances of having a leak. The basic premise is that it only requests sufficient power and flow temperature from the boiler to achieve or maintain the desired room temperature, and this is how it brings about energy savings. It keeps the boiler in condensing mode for longer and reduces cycling. On some controllers you can manually limit the maximum flow temperature it can request, so worth looking at that if it's desirable for you. Your WB is eminently repairable though and provided you look after it well with regular servicing there's no reason why it shouldn't last another 10 years or more. You don't even know if the Ideal Vogue will still be in production by then, so it's rather pointless planning ahead to fit one.
But if you want to buy unicorn pee , I sell a gallon for £135 will make your system 100% efficient and you will never need to pay for gas again, honest it works
Personal experience says that open therm is better and worthwhile having with the correct boiler and controller.

It's not going to save you loads, you might not even get the expense back for a while, but the house is more comfortable.

I had a condensing boiler before fitted with a on off thermostat, the heating overshoot was immense, and I've noticed a significant drop in the cost of my heating since installing the intergas and opentherm.

I wouldn't go with ideal halo stat though, from what I hear it's clunky with poor support.

I don't think the ideal let alternative stats use the opentherm within the boiler.

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