System boiler recommendations (hot water priority ~5kW heatloss)

[SpecialK]

Hi,
I am looking to replace my combi boiler (Vaillant ecotec 831) with a system boiler and unvented cylinder.

I have a mixergy 180L cylinder ready to go but I would like some suggestions as to which system boiler to pair it to?

I have a heat loss of approx. 5kW.

Ideally the boiler will have open therm / weather compensation and the ability to call hot water heating at a different temperature.

There are two heating loops. One is UFH in an extension and the other is the radiators in the rest of the house.

Would an Ideal Vogue S15kw be a good choice?

I wouldn't mind another Vaillant but the price of the controls are off putting.

Anything else I should add to the wish list? Best system filters? Is it worth splitting the upstairs and downstairs heating loops?

Thanks!

 

[drives]

Ashp?

 

[vulcancontinental]

The heat loss is quite low so you'll want a boiler that can modulate low to avoid as much cycling as possible. Check whether the boiler can be range rated (restrict its maximum heating output) and how low can it modulate that output too. Not all boilers can use WC and OpenTherm together. Separating hot water reheat, priority domestic hot water (PDHW) can be done within the boiler or external to the boiler by the control system.

 

[martygturner]

Make sure that you get an opentherm thermostat that actually works with you choice of boiler, there are many implementations of opentherm. I was stung by worcester bosch who intial advertised a greenstar 8000 as opentherm , then said it was compatible vi a modual that did not exist in the uk, had to get one from the Netherlands.

 

[SpecialK]

The heat loss is quite low so you'll want a boiler that can modulate low to avoid as much cycling as possible. Check whether the boiler can be range rated (restrict its maximum heating output) and how low can it modulate that output too. Not all boilers can use WC and OpenTherm together. Separating hot water reheat, priority domestic hot water (PDHW) can be done within the boiler or external to the boiler by the control system.

Thanks, I will have to check to see if opentherm and weather comp can be used together. Otherwise I will have to pick a suitable thermostat that will do both!

The ideal S15 does 4.9kW part load. Veismann seem to go lower but they seem overly expensive?

(actually the S15 goes down to 3kW central heating which is better!)

 

[SpecialK]

Make sure that you get an opentherm thermostat that actually works with you choice of boiler, there are many implementations of opentherm. I was stung by worcester bosch who intial advertised a greenstar 8000 as opentherm , then said it was compatible vi a modual that did not exist in the uk, had to get one from the Netherlands.

One to avoid then! I know you can get opentherm for Vaillant too but its costly. Opentherm should be available on all new boilers!

 

[SpecialK]

Ashp?

I was thinking about it but octopus etc want too much money. Cheaper to get a gas boiler!

 

[Mister Banks]

What about a Vokera Pinnacle S, I think they modulate very low.

 

[vulcancontinental]

Thanks, I will have to check to see if opentherm and weather comp can be used together. Otherwise I will have to pick a suitable thermostat that will do both!

The ideal S15 does 4.9kW part load. Veismann seem to go lower but they seem overly expensive?

(actually the S15 goes down to 3kW central heating which is better!)

They can but not always, so much depends on the boiler. I ran trials at home on my system and found around a 1% advantage in both together but comfort was smoother with WC alone on a simple timer switching from a comfort temperature to a setback temperature overnight or when we're both out.

If PDHW control and valving is not inbuilt in the boiler look at EPH controls, I've used it very successfully PDHW OpenTherm in a property I let, DHW and two heating zones. Can be controlled by app too.

4.9kW minimum on the Ideal is what your property can absorb, probably a little less, when the temperature outside is -3°C. That temperature forms a very small part of the heating season, usually it's 5-9°C so constant cycling cannot be avoided. Check if there's an adjustable anti-cycle delay on the boiler, that would help.

The Vokera Pinnacle 25S modulates lower than any boiler on the market and has many features that can be configured to add value however be aware I work for the company.

 

[drives]

I was thinking about it but octopus etc want too much money. Cheaper to get a gas boiler!

It may be a bit cheaper but I can't imagine by much, by the time you've factored in the cylinder install cost as well? Octopus weren't the cheapest for us and their prices have gone up quite a lot recently.

 

[SpecialK]

It may be a bit cheaper but I can't imagine by much, by the time you've factored in the cylinder install cost as well? Octopus weren't the cheapest for us and their prices have gone up quite a lot recently.

Thanks ... I probably should get some more quotes for a heat pump... but I am not sure I am ready to switch yet. I even have solar and a large battery.
Octopus want £5.3k or £7.4k depending on type. To be honest if I got them to survey I bet it would drop in price a lot.

I already have the mixergy installed as I previously heated it with solar and ran it instead of the combi in the summer! Now I get paid for export its not worth diverting. I want to get rid of the combi to make more room upstairs so will switch to a system boiler for now.

 

[SpecialK]

They can but not always, so much depends on the boiler. I ran trials at home on my system and found around a 1% advantage in both together but comfort was smoother with WC alone on a simple timer switching from a comfort temperature to a setback temperature overnight or when we're both out.

If PDHW control and valving is not inbuilt in the boiler look at EPH controls, I've used it very successfully PDHW OpenTherm in a property I let, DHW and two heating zones. Can be controlled by app too.

4.9kW minimum on the Ideal is what your property can absorb, probably a little less, when the temperature outside is -3°C. That temperature forms a very small part of the heating season, usually it's 5-9°C so constant cycling cannot be avoided. Check if there's an adjustable anti-cycle delay on the boiler, that would help.

The Vokera Pinnacle 25S modulates lower than any boiler on the market and has many features that can be configured to add value however be aware I work for the company.

Thanks I will take a look at the Vokera. I'm fed up of heating my Vaillant cycling as it has a minimum of about 9kW so it doesn't like it when just the UFH is on!
Those EPH controls look good.

 

[drives]

Thanks ... I probably should get some more quotes for a heat pump... but I am not sure I am ready to switch yet. I even have solar and a large battery.
Octopus want £5.3k or £7.4k depending on type. To be honest if I got them to survey I bet it would drop in price a lot.

I already have the mixergy installed as I previously heated it with solar and ran it instead of the combi in the summer! Now I get paid for export its not worth diverting. I want to get rid of the combi to make more room upstairs so will switch to a system boiler for now.

Wow ok. HP ready cylinder, battery, solar….and you still want to put a boiler in?

We already had the cylinder installed and it just wouldn’t compute with the likes of octopus who would give us a standard price. There are some decent cheaper ashps as well….the vaillant quotes were quite expensive.

 

[Mister Banks]

Panasonic heat pumps seem to get good reviews online and are one of the cheaper heat pumps. Maybe you could buy the heat pump and then pay a plumber and electrician to do the installation, forget about the BUS grant.

 

[drives]

Panasonic heat pumps seem to get good reviews online and are one of the cheaper heat pumps. Maybe you could buy the heat pump and then pay a plumber and electrician to do the installation, forget about the BUS grant.

But why would anyone write off 7.5k? Plenty of independents are mcs registered, and who won’t just quote a 7kw or 10kw vaillant as standard.

Crazy imo to have a large storage battery as well and not at least get a bespoke quote. Plus low heat losses as well and the ashp can modulate to lower flow temps, perfectly suited to weather comp. You will be saving many hundreds if not thousands of pounds a year, and more future proof. I thought the blocker was going to be something like outdoor space.