TRV‘s

ThisIsWeird

I'm guessing that some modern boilers will now have that facility for just that reason - they've worked out that a too-low output temp for economic reasons could lead to bugs in the tank.

Do you know if it's a regulatory requirement to have a 'dual' output, FreeBear?

Auti

This is how my boiler looks so don‘t understand re boiler flow temp. I have a thermostat on the DHW tank in airing cupboard which is heated by gas - no electric immersion heater.  Presume the dial dots correspond to temps maybe but not a scooby what they might correspond to.

ThisIsWeird

Make and exact model, Auti?
It does appear to have only a single output temp. 
The range will likely be something like 30o to 80+. Probably currently in the mid-60s.

FreeBear

Albermarle said:

FreeBear said:

Albermarle said: One caveat being that if it is not a combi boiler, then you should not turn the boiler temperature down too far, as your hot water will not get hot enough.

With a system or heat only boiler, hot water should take priority and boost the flow temperature accordingly.

I did not know that. I am pretty sure when I turn the boiler ( system)  flow temperature down, the hot water does not seem quite so hot. However I have never done a scientific test.

Not all boilers & controls support priority DHW. This post explains it a bit better - https://lhsplumbing.com/blogs/news/priority-domestic-hot-water-pdhw

And if you have an OpenTherm compatible boiler, EPH offer a kt for use with their controls - https://www.ephcontrols.co.uk/section/pdhw/

A side note - With a combi boiler, I run a flow temperature of around 52°C, yet when DHW is called for, the boiler temperature rises to 60°C. Ruins efficiency, so I try to limit the amount of hot water I use.

ThisIsWeird said: Do you know if it's a regulatory requirement to have a 'dual' output

And no, I do not believe PDHW (or dual temperatures) is a regulatory requirement (at least in a domestic setting). But boiler and control manufacturers are aware of the issue, and many offer boilers/controls with the feature built in.

Auti

@ThisIsWeird - it is Ideal Icos HE24  installed 03.04.2006 has had a new PCB (decided to go 2 days before xmas 3 or so yrs ago) but otherwise a very well behaved boiler. 

ThisIsWeird

Thanks FreeBear.

Auti, yes, a simple and straight-forward boiler, non-condensing, little to go wrong, but no way to handle the desired separate DHW and CH conundrum.
I'd still be inclined to go 'large' with any rads you can, since this is the 'cheapest' time to do so as they need replacing anyway. They won't over-heat a room, as they'll simply be tweaked down to act like their predecessors with the existing boiler.
At some point, tho', your boiler will need replacing...

Auti

ThisIsWeird - I think it is a condensing boiler as that was what I was told?

ThisIsWeird

Auti said:

ThisIsWeird - I think it is a condensing boiler as that was what I was told?

Could be!* Does it have a white plastic 22mm pipe existing from underneath, heading out through t'wall?

If it's condensing, then even more reason to go 'large'... Actually, it'll make little/no difference until you can turn the supply temp down.

It's just a general suggestion I, and others, make on the forum, whenever folk are changing rads. If you have an eye on the future, then please consider 'large'. I fully understand if folk don't want fatter or larger rads in their rooms, but - especially if this is their 'forever' home - then, well, you know...

In essence, if you do change to an alternative energy supply in the future, then good chance all your current rads will be declared 'undersized'. But, technology changes.

Edit: *Yes, it is :-) 90% eff.

FreeBear

ThisIsWeird said: It's just a general suggestion I, and others, make on the forum, whenever folk are changing rads. If you have an eye on the future, then please consider 'large'. I fully understand if folk don't want fatter or larger rads in their rooms, but - especially if this is their 'forever' home - then, well, you know...

In essence, if you do change to an alternative energy supply in the future, then good chance all your current rads will be declared 'undersized'. But, technology changes. 

But... If your CH is plumbed with micro-bore pipes (8mm or 10mm), it will need to ripped out and replaced with bigger pipes. Heat pumps and low temperature gas boilers need bigger pipes to allow for greater volumes of water to be pumped round the system. This typically means 22mm or even 28mm for the main feed/returns, and short runs of 15mm to the radiators.

Auti

Hmmmmm more questions to ask plumber - this is top of boiler and other picture is in airing cupboard vaguely think when magfilter mentioned he said something about 28 (larger pipe size) needed but could be wrong. (Do need to do some dusting)