So many thermal store questions!

[SimonB27]

So the plan is this. Currently I have all rooms individually controllable through programmable TRVs allowing me to heat only the rooms that are being used on different profiles during the day and night. So far so good.

But I have three main problems with my boiler.

1. there is no boiler interlock with my TRV system so I have one rad permanently on and the room stat turns off the boiler when that area gets too hot. That is not efficient and might mean other areas are too cold. This issue is solvable but I might not need to if I go for a thermal store.

2. it is a combi boiler which, despite promises when it was installed, is not capable of running a bath and a shower at the same time and

3. it's not working properly anyway in spite of several maintenance visits so I'm sick of it.

The question is what do I replace it with?

Ideally I'd like a thermal store system. This would solve a number of issues:

- Boiler interlock is no longer a problem that needs to be dealt with because the boiler heats the store and the store pumps to the radiators.

- a system heat only boiler is simpler and presumably therefore cheaper and

- I get mains pressure hot water - yippee!

BUT...

I am constrained in that the boiler (and where the hot water tank used to be many years ago) is in an airing cupboard so I am limited by how big the thermal store can be. The house has five bedrooms and three reception rooms and is old (and therefore drafty) It is adequately heated though by the current 33kW boiler. I think a 250l thermal store is as big as I can fit without potentially relocating it to the cellar, which is a bigger job. Is that anything like big enough for my needs?

So far I've seen (if I remember correctly) thermal stores that pump the stored water through the boiler or heat the store indirectly via a coil and also ones that pump the stored water round the rads or heat that indirectly via a coil. I understood stratification was a key element of a thermal store. Is one type better than the other?

I've also seen systems that heat the DHW using an external heat exchanger (which will fail if the power goes off) and
ones that pass DHW through a coil. The manufacturers of each type of course swear theirs is best.

Finally vented or unvented, sealed boiler systems or not? Frankly the one thing I do like about my current setup is doing away with the header tank although the system does very gradually lose pressure and has done so while we've been away on holiday so we've come back to a cold house. If both the boiler and the rad system were sealed then I guess I'd be looking at two pressure vessels although one might be integral to the boiler.

I am confused by so much choice. Do I (can I?) go for a thermal store or do I go for a regular system boiler and go back to having a hot water tank for DHW only or do I go for something like a Viessmann Vitodens 111W, which has an integrated storage tank and promises that it can indeed fill a bath and run a shower at the same time (I only found out about this today!).

So many choices. I'd be very grateful if the experts here could shed a little light on what's good and what's bad

 

[Rob Foster]

Why not keep,your combi, put the cenheating flow through a cylinder as well as the rads, top up the cylinder with some solar thro a 2nd coil. Instant hot downstairs and stored hot elsewhere. It’s not rocket science we were doing this in the late 8o,s when combis were all new. If you want a diagram I am sure someone on here will have one let us know more do

 

[AMGasServices]

Go with a smart room stat and smart radiator controls you can control each room individually.

 

[SimonG]

Only a thermal store for multiple heat inputs. Unvented cylinder run off the combi

 

[ShaunCorbs]

whats the mains flow and pressure like with an outlet open?

 

[Best]

Unvented cylinder best solution if possible.
A sealed system boiler or use a combi which will have the advantage of hot water direct from boiler to one or more nearby taps etc and rest of house also having mains hot water, but supplied from unvented cylinder

 

[Rob Foster]

We have a new system on line soon that dispenses with trv and zone valves but allows total control over the heating system it is a beano and oh so simple, it can be retro fitted or installed alongside hive or the strawberry system. Watch out grundfos we are coming to get you....or more accurately my South Korean partners are landing soon they have more lolly than me

 

[SimonB27]

Go with a smart room stat and smart radiator controls you can control each room individually.

I'm well ahead on that already. Each rad has its own digital TRV that stores its own weekely schedule. All controllable centrally. The rooms are already smart enough. It's the heating of the water that needs to be a bit cleverer.

 

[SimonB27]

We have a new system on line soon that dispenses with trv and zone valves but allows total control over the heating system it is a beano and oh so simple, it can be retro fitted or installed alongside hive or the strawberry system. Watch out grundfos we are coming to get you....or more accurately my South Korean partners are landing soon they have more lolly than me

I'm not familiar with Strawberry - can you point me in the right direction?

How does the system control individual rooms? What I'm trying to get away from is systems like Hive or Nest that claim to be "smart" but actually are still mostly heating your whole house or none of it. I'm already well past that. I have five bedrooms and three reception rooms, only a small proportion of which are being used at any one time unless we have guests at a weekend. I'm saving a fortune by only heating rooms when they are being used but the way my water is heated is not really keeping up with the rest of the system.

 

[SimonB27]

Why not keep,your combi, put the cenheating flow through a cylinder as well as the rads, top up the cylinder with some solar thro a 2nd coil. Instant hot downstairs and stored hot elsewhere. It’s not rocket science we were doing this in the late 8o,s when combis were all new. If you want a diagram I am sure someone on here will have one let us know more do

The combi is really unreliable. It trips at regular intervals in spite of being fixed regularly and it has no control over the DHW temperature which is usually far too hot. It's been looked at for these problems more times than I can recall but they recur.

If I'm looking at a new boiler would it just be simpler to go for a heat only system boiler and go back to a cylinder? Solar's not realy an option unfortunately. Trees in the way, roof slopes the wrong way and listed building!

 

[gmartine]

If I'm looking at a new boiler would it just be simpler to go for a heat only system boiler and go back to a cylinder?

Or system boiler, yes.

 

[SimonB27]

I guess the main driver for this is the fact that I have a 33kW boiler and gradually, as the house comes up to temperature, it's pushing its heat out into fewer and fewer rads. At the limit, it might have one rad with its valve at say 50% before the boiler interlock (that I have yet to install) kicks in and switches the boiler off. Even at its minimum, the boiler is going to be kicking out close to 5kW.

I quite fancy the buffer concept of a thermal store - hence my original question - that will stop the boiler cycling quite so much.

On the other hand an Opentherm boiler could help here where I can reduce the water temperature as the house gets up to heat. That throws another possibility into the mix.

So many options!

 

[Rob Foster]

I'm not familiar with Strawberry - can you point me in the right direction?

How does the system control individual rooms? What I'm trying to get away from is systems like Hive or Nest that claim to be "smart" but actually are still mostly heating your whole house or none of it. I'm already well past that. I have five bedrooms and three reception rooms, only a small proportion of which are being used at any one time unless we have guests at a weekend. I'm saving a fortune by only heating rooms when they are being used but the way my water is heated is not really keeping up with the rest of the system.

You cannot have the system yet we are still building the boards and software the pumps are sorted ....note pumpS but it will be a beano

 

[sammathias]

Your boiler must be cycling a hell of alot?

 

[gmartine]

As you trim down your heating requirements considerably (compared to the size of the house) an answer would be to cascade two boilers (with an unvented cylinder), that way the one single boiler can modulate right down to the few kw you need for heating tick over and the second boiler can kick in when more capacity is required. To be honest a well sorted large boiler installation with weather comp will probably also do but a thermal store is not the answer, they are inherently inefficient and as previously mentioned ideally require more than one heat source.

 

[SimonB27]

an answer would be to cascade two boilers (with an unvented cylinder)

That's a creative solution but space constraints dictate that two boilers is not really on. I have found one (Viessmann) that will modulate itself down to 1.8kW from a maximum of 35kW (a ratio of 19:1!), which is impressive.

but a thermal store is not the answer, they are inherently inefficient.

Ah! Now we're getting to the crux of my question - is a thermal store actually a good idea or not? Why do you say they are less efficient? I can see there's a delay in heating up your house if you're starting from scratch but if the store is warm then heat in = heat out. I'm just buffering am I not?

I was hoping there would be an advantage in the boiler not cycling so much because it's not having to cope with anything between 15 rads and one and potentially I was thinking I might have the boiler spending more time in condensing mode if the return is from the bottom of the store rather than the rads.

Thanks for your comments. I appreciate there may be so many other factors I have not thought about.

 

[gmartine]

It wouldn't cycle so much that's true but you don't currently have a functioning interlock to prevent dry cycling.
A particular issue with the way you want to use the store is that you have to heat it above the temperature required by the radiators typically by at least 10 degrees + that isn't an issue if the store is supplemented by solar or a back boiler etc but that's another 10 + deg you're paying for directly obviously. That Viessmann with weather comp looks to be a good option, a couple of kw is perhaps 2-3 rooms just don't trim down the temp profile of each room just because you can as a house full of cold spots isn't desirable either. Assuming you have more than one bathroom/HW outlet most would right in recommending an unvented cylinder but a large storage combi (SC) may just about provide the HW for your needs too if space is an issue. Get a decent engineer to do the heat loss calcs for your home and HW demand before deciding anything.

Viessmann Vitodens 222-F 35kW Storage Combination Boiler Natural Gas ErP with Weather Compensation Controller | Boilers

 

[dan_the_plumber]

So the plan is this. Currently I have all rooms individually controllable through programmable TRVs allowing me to heat only the rooms that are being used on different profiles during the day and night. So far so good.

But I have three main problems with my boiler.

1. there is no boiler interlock with my TRV system so I have one rad permanently on and the room stat turns off the boiler when that area gets too hot. That is not efficient and might mean other areas are too cold. This issue is solvable but I might not need to if I go for a thermal store.

2. it is a combi boiler which, despite promises when it was installed, is not capable of running a bath and a shower at the same time and

3. it's not working properly anyway in spite of several maintenance visits so I'm sick of it.

The question is what do I replace it with?

Ideally I'd like a thermal store system. This would solve a number of issues:

- Boiler interlock is no longer a problem that needs to be dealt with because the boiler heats the store and the store pumps to the radiators.

- a system heat only boiler is simpler and presumably therefore cheaper and

- I get mains pressure hot water - yippee!

BUT...

I am constrained in that the boiler (and where the hot water tank used to be many years ago) is in an airing cupboard so I am limited by how big the thermal store can be. The house has five bedrooms and three reception rooms and is old (and therefore drafty) It is adequately heated though by the current 33kW boiler. I think a 250l thermal store is as big as I can fit without potentially relocating it to the cellar, which is a bigger job. Is that anything like big enough for my needs?

So far I've seen (if I remember correctly) thermal stores that pump the stored water through the boiler or heat the store indirectly via a coil and also ones that pump the stored water round the rads or heat that indirectly via a coil. I understood stratification was a key element of a thermal store. Is one type better than the other?

I've also seen systems that heat the DHW using an external heat exchanger (which will fail if the power goes off) and
ones that pass DHW through a coil. The manufacturers of each type of course swear theirs is best.

Finally vented or unvented, sealed boiler systems or not? Frankly the one thing I do like about my current setup is doing away with the header tank although the system does very gradually lose pressure and has done so while we've been away on holiday so we've come back to a cold house. If both the boiler and the rad system were sealed then I guess I'd be looking at two pressure vessels although one might be integral to the boiler.

I am confused by so much choice. Do I (can I?) go for a thermal store or do I go for a regular system boiler and go back to having a hot water tank for DHW only or do I go for something like a Viessmann Vitodens 111W, which has an integrated storage tank and promises that it can indeed fill a bath and run a shower at the same time (I only found out about this today!).

So many choices. I'd be very grateful if the experts here could shed a little light on what's good and what's bad

Hi Simon. What size is your rising cold main please?

 

[Belli]

As far as I can see from reading the original post why don't you try moving the stat to colder part of house obvs not to close to a rad or trv side at least of a rad first, then just add a zone and add unvented for hot water if mains is up to it, when boiler gives up in a few years go to system boiler.
[automerge]1569709699[/automerge]

As far as I can see from reading the original post why don't you try moving the stat to colder part of house obvs not to close to a rad or trv side at least of a rad first, then just add a zone and add unvented for hot water if mains is up to it, when boiler gives up in a few years go to system boiler.

Just seen how old this is ignore! Sat beer!!!

 

[Allgoode]

Sort out your draughts & get some insulation in first before you pour money needlessly down the drain.
Once them x2 issue's are sorted then move forwards wrt the water/heating.
As mentioned above if your combi boiler is ok for the heating side then link it in through a decent sized unvented cylinder & if you can have PV cells on the house then have an immersion running & eventually maybe even battery back up.
Cheers,
Andy