CH boiler replacement, comments/advice please including on Hive and alternatives.

Rollinghome

Our antique gas boiler, maybe 40 years old, has finally given up, so it and controls etc needs replacing asap. (Probably just blocked pilot but...) Any comments or suggestions really welcome.

The house is 4 bed detached with 9" solid walls and a lot of single-glazed windows that need replacing, so needs a lot of heat. The current system is open vent with pumped CH and gravity HW. The boiler is floor-standing under a kitchen worktop with a balanced flue - which still looks the best option for position. The only controls are a dodgy programmer and TRVs on all rads bar two smallest bedrooms. No room- or cylinder-stats fitted.

The boiler is likely to be a Vailant ecoFIT Pure 425 which is a regular boiler with a rear flue and should fit under the worktop.  

It's a bit tucked away for front controls so remote controls preferable. I was considering getting a Hive thermostat but not totally clear on how it works. I assume the schedule periods are infinitely adjustable minute by minute and it will give me independent control of CH and HW temp and timings?  Is it preferable to a conventional programmer and room-stat or something else?

Is there anything else I should consider?  I've also got a spare brand-new bells and whistles, 7 day etc single channel Sangamo Quarzmaster E850 time-clock if that could do anything useful.

Any suggestions on getting estimates welcomed too!.

 

FreeBear

Rollinghome said: The boiler is likely to be a Vailant ecoFIT Pure 425 which is a regular boiler with a rear flue and should fit under the worktop.

Check the minimum output to central heating - Good boilers will modulate down to around 3.2kW. This will reduce short cycling which will improve reliability and efficiency.

Pick a boiler that supports OpenTherm, and you can then pair it with a smart programmable thermostat - This will allow you to vary flow temperature automatically, which helps with efficiency. Vaillant has it's own OpenTherm type interface, but controls that interface to their boilers are few & far between.

With an open vented system, you are going to need to do some replumbing - Well worth fitting larger radiators all round and increasing the diameter of the pipes where possible.

Whilst you could retain the existing hot water tank, upgrading to an unvented tank would give you mains pressure hot water - You also want to ensure that the controls & boiler can do priority DHW - In a nut shell, automatically runs the boiler at a higher flow temperature when heating the tank up, and drops back down for central heating.

Once you've priced up the work above, compare the cost to having a heat pump installed - You may find the difference is minimal.

I replaced a 40+ year old Baxi back boiler in 2023. Replumbed the system with 15/22mm pipe and fitted oversized radiators with an eye on installing a heat pump in the future. This has enabled me to run the gas boiler at relatively low flow temperatures (40-60°C). In doing so, getting efficiencies of 92-96% which is helping to keep the gas bill down. If I had waited until last year, I would have (probably) gone for a heat pump. Once the cost of radiators & plumbing is taken in to account, a HP would have been a little cheaper.

Rollinghome

FreeBear said:

Rollinghome said: The boiler is likely to be a Vailant ecoFIT Pure 425 which is a regular boiler with a rear flue and should fit under the worktop.

Check the minimum output to central heating - Good boilers will modulate down to around 3.2kW. This will reduce short cycling which will improve reliability and efficiency.

Pick a boiler that supports OpenTherm, and you can then pair it with a smart programmable thermostat - This will allow you to vary flow temperature automatically, which helps with efficiency. Vaillant has it's own OpenTherm type interface, but controls that interface to their boilers are few & far between.

With an open vented system, you are going to need to do some replumbing - Well worth fitting larger radiators all round and increasing the diameter of the pipes where possible.

Whilst you could retain the existing hot water tank, upgrading to an unvented tank would give you mains pressure hot water - You also want to ensure that the controls & boiler can do priority DHW - In a nut shell, automatically runs the boiler at a higher flow temperature when heating the tank up, and drops back down for central heating.

Once you've priced up the work above, compare the cost to having a heat pump installed - You may find the difference is minimal.

I replaced a 40+ year old Baxi back boiler in 2023. Replumbed the system with 15/22mm pipe and fitted oversized radiators with an eye on installing a heat pump in the future. This has enabled me to run the gas boiler at relatively low flow temperatures (40-60°C). In doing so, getting efficiencies of 92-96% which is helping to keep the gas bill down. If I had waited until last year, I would have (probably) gone for a heat pump. Once the cost of radiators & plumbing is taken in to account, a HP would have been a little cheaper.

Thanks FB.

I was going for the Vailant ecoFIT Pure 425 because its dimensions and rear flue would allow fitting in that position and has a good reputation. The house is fairly eccentric with the kitchen built around the boiler and otherwise that space would go unused with few other options.

Tubes are 28/22/15 mm and the rads are a good size.  We considered a heat pump but being detached with solid walls, big bay windows front and rear, and suspended polished hardwood floors mostly without fitted carpets, it would be very expensive to well insulate.  At our advanced age, the extra cost is unlikely to be recouped.

I haven't concentrated too much on the efficiency of the Vaillant, I'm already blurry-eyed reading the literature, but assume that with its price and reputation it will be decent. We've already got used to high bills as the price for living in a house that's too big for us. And with no heating now, it's fairly urgent.

Any experience of the Hive?

FreeBear

Rollinghome said: Tubes are 28/22/15 mm and the rads are a good size.  We considered a heat pump but being detached with solid walls, big bay windows front and rear, and suspended polished hardwood floors mostly without fitted carpets, it would be very expensive to well insulate.  At our advanced age, the extra cost is unlikely to be recouped.

Any experience of the Hive?

A heat pump is just another source of heat. Yes, a property needs a decent level of insulation, but that applies regardless of what you use to provide the heat.

As mentioned earlier, I fitted a gas boiler, but have also spent quite a bit of time improving insulation levels - A late 1920s 3 bed semi, so not the best performing property. However, I'm on target to use 2500kWh of gas this year (down from ~8000kWh when I started). Not likely to recover the total cost, but the improvement in comfort levels make up for it.

No experience of Hive, Nest, or any of the other "off the shelf" controls. I'm using Home Assistant with some custom hardware to control & monitor the heating.

ThisIsWeird

Hi Rollinghome.
The Vaillant is one of many reputable makes, so if you like this model, and it fits in the space most neatly and easily, then great. They will all be significantly more efficient than your current beast.
I have to agree that a Heat Pump would be a very risky install here, given all you've said about the insulation levels. There is simply no reason to be cold, or to have energy bills that will be similar - or possibly even higher - than what a modern gas boiler will provide, especially when it'll cost more and look more ugly.
That leaves the controls. You have an E850?! Wow. Stick it on eBay... Someone will want it to replace a defunct one, but it'll have no place with your new boiler
The Hive is one of many Smart systems, and it'll transform the control you'll have over your CH and DHW. However, you should go for a model that uses the Vaillant protocol, as this will squeeze out a bit more efficiency. Not sure what's recommended, but - yes - they will do what you suspect; full control over the timings for your CH, with whichever temp you want for each time slot. Instant override from your phone. Going out for the day? Just turn the CH down, and then back up by phone as you head home. Smart is fab.
You might even consider adding Smart TRV heads on the most regularly used rads, such as in bedrooms. That'll then control them to just come on for a bit before bedtime, and again before you wake up - and off (or right down) at other times. Instant savings.
A quick surf suggests Vaillant uses eBUS, and have their own VSmart controls, but no idea what it's like, or alternatives. Should be quite researchable.

Albermarle

I think you need to be clear on the hot water situation.
Gravity fed is very old fashioned, and I think you should be at least looking at the HW being a pumped system as well.
Or as already mentioned you could move to an unvented system for CH and HW.
This would mean no more tanks in the attic and mains pressure for showers etc.
However you would need a new HW tank, and it will mean more cost/pipework to install as it is a more specialised job to install them.
Even if you stick to a vented system, it would probably be a good idea to have a new HW tank anyway, if yours is quite old. Just replacing a hot water tank like for like ( but a more modern well insulated one is not such a big/costly job.

Despite you having a four bed solid wall house, the boiler you have picked seems more powerful than necessary at 25KW. It looks like it can only modulate down to 6KW so will use more gas than a smaller boiler. 
We have a 4 bed semi with solid walls. Double glazed, but some of it quite old. Open fire and draughty hallway.
Our 18 KW boiler copes with no issues. 13 radiators + hot water.

silvercar

Our hive controls when the heating and hot water are on or off. The actual temperature of the water in the rads/ water from the taps is controlled by the boiler. When the heating is scheduled on by the app, the hive room thermostats turn it off if the thermostat reaches the required temperature. 
You can have 6 on and offs each day, with different temperatures for each. So we have a slightly lower temperature in the early morning and early afternoon than we do late evening. Other times it is set very low for frost protection, but never reaches that low.

Advantages for us is the ability to switch the heating on or off when we are out and to turn the heating off when we are on holiday, knowing we can turn it on before we arrive home.

Rollinghome

ThisIsWeird said:

Hi Rollinghome.
The Vaillant is one of many reputable makes, so if you like this model, and it fits in the space most neatly and easily, then great. They will all be significantly more efficient than your current beast.
I have to agree that a Heat Pump would be a very risky install here, given all you've said about the insulation levels. There is simply no reason to be cold, or to have energy bills that will be similar - or possibly even higher - than what a modern gas boiler will provide, especially when it'll cost more and look more ugly.
That leaves the controls. You have an E850?! Wow. Stick it on eBay... Someone will want it to replace a defunct one, but it'll have no place with your new boiler
The Hive is one of many Smart systems, and it'll transform the control you'll have over your CH and DHW. However, you should go for a model that uses the Vaillant protocol, as this will squeeze out a bit more efficiency. Not sure what's recommended, but - yes - they will do what you suspect; full control over the timings for your CH, with whichever temp you want for each time slot. Instant override from your phone. Going out for the day? Just turn the CH down, and then back up by phone as you head home. Smart is fab.
You might even consider adding Smart TRV heads on the most regularly used rads, such as in bedrooms. That'll then control them to just come on for a bit before bedtime, and again before you wake up - and off (or right down) at other times. Instant savings.
A quick surf suggests Vaillant uses eBUS, and have their own VSmart controls, but no idea what it's like, or alternatives. Should be quite researchable.

Yes, a brand spanking new E850 still in it's box. Too good just to put the kettle on in the mornings. I'm not into Ebay but will certainly take a look.   I've also got a lovely brand new SMC Commander pump in its box. Would be sure to outlast any modern one.  Both pressies to my wife during her 40 years in an architects practice.  More useful than samples of bricks.

Thanks for your views on the Hive and other suggestsions.  I'm just writing out a flexible quote for an installer so will probably suggest the Hive and leave the techie compatability details to them..  

I'm not going to install this system myself though I have installed a couple of full systems back in the day when they weren't so fussed about us amateur DIYers blowing up the street, and under instruction from my wife on the proper way to spec radiators etc.

Would have been nice if the boiler had gone down in July instead of January. Was on my to-do list 10+ years ago.

ThisIsWeird

Rollinghome said:

ThisIsWeird said:

Hi Rollinghome.
The Vaillant is one of many reputable makes, so if you like this model, and it fits in the space most neatly and easily, then great. They will all be significantly more efficient than your current beast.
I have to agree that a Heat Pump would be a very risky install here, given all you've said about the insulation levels. There is simply no reason to be cold, or to have energy bills that will be similar - or possibly even higher - than what a modern gas boiler will provide, especially when it'll cost more and look more ugly.
That leaves the controls. You have an E850?! Wow. Stick it on eBay... Someone will want it to replace a defunct one, but it'll have no place with your new boiler
The Hive is one of many Smart systems, and it'll transform the control you'll have over your CH and DHW. However, you should go for a model that uses the Vaillant protocol, as this will squeeze out a bit more efficiency. Not sure what's recommended, but - yes - they will do what you suspect; full control over the timings for your CH, with whichever temp you want for each time slot. Instant override from your phone. Going out for the day? Just turn the CH down, and then back up by phone as you head home. Smart is fab.
You might even consider adding Smart TRV heads on the most regularly used rads, such as in bedrooms. That'll then control them to just come on for a bit before bedtime, and again before you wake up - and off (or right down) at other times. Instant savings.
A quick surf suggests Vaillant uses eBUS, and have their own VSmart controls, but no idea what it's like, or alternatives. Should be quite researchable.

Yes, a brand spanking new E850 still in it's box. Too good just to put the kettle on in the mornings. I'm not into Ebay but will certainly take a look.   I've also got a lovely brand new SMC Commander pump in its box. Would be sure to outlast any modern one.  Both pressies to my wife during her 40 years in an architects practice.  More useful than samples of bricks.

Thanks for your views on the Hive and other suggestsions.  I'm just writing out a flexible quote for an installer so will probably suggest the Hive and leave the techie compatability details to them..  

I'm not going to install this system myself though I have installed a couple of full systems back in the day when they weren't so fussed about us amateur DIYers blowing up the street, and under instruction from my wife on the proper way to spec radiators etc.

Would have been nice if the boiler had gone down in July instead of January. Was on my to-do list 10+ years ago.

I have a Hive myself, and like it, but I wouldn't recommend it for the Vaillant as this boiler will accept a more nuanced control which should add a couple more % efficiency.
The essential difference is that the Hive will give you full control over times and temps, and is nice to use, but 'all' it'll ultimately do is turn the boiler on and off at your chosen times, a bit like a better version of your existing room stat.
An eBUS, or Opentherm, or other more advanced Smart control will do a bit more; as the required temp approaches, it'll inform the boiler that it's 'close', and tell the boiler to turn down to match this reduced demand. So, instead of on...on...on...on...ok, off...off...off...right, on...on...etc, it'll be like, on...on...ooh, getting close, back off, turn down, eeeassssyyy now, that's it, hooooold it...niiiice, ookkaaay, turn it back up a bit more...
So, it'll not only mean fewer ones and offs for the boiler, but it'll try and keep the boiler more in the 'condensing' area for longer = more efficiency.
It would be silly to not go for this - all these Smart controls cost a similar amount in the first place.

Rollinghome

Albermarle said:

I think you need to be clear on the hot water situation.
Gravity fed is very old fashioned, and I think you should be at least looking at the HW being a pumped system as well.
Or as already mentioned you could move to an unvented system for CH and HW.
This would mean no more tanks in the attic and mains pressure for showers etc.
However you would need a new HW tank, and it will mean more cost/pipework to install as it is a more specialised job to install them.
Even if you stick to a vented system, it would probably be a good idea to have a new HW tank anyway, if yours is quite old. Just replacing a hot water tank like for like ( but a more modern well insulated one is not such a big/costly job.

Despite you having a four bed solid wall house, the boiler you have picked seems more powerful than necessary at 25KW. It looks like it can only modulate down to 6KW so will use more gas than a smaller boiler. 
We have a 4 bed semi with solid walls. Double glazed, but some of it quite old. Open fire and draughty hallway.
Our 18 KW boiler copes with no issues. 13 radiators + hot water.

Yes it is a bit old-fashioned now, so with the new boiler the system will be fully pumped. The only time gravity feed feed was a blessing was if the pump fails. And pumps don't fail if you get a good one.

I'm sticking with an unvented "regular boiler" system because I don't want any additional stress on an old system I would get from a closed system combi or system boiler.  With a combi, I'd get much lower water pressure because we have a raised storage tank and very low mains pressure.

Our old boiler is 80 btu so 25 Kw is very similar and big enough for a fast warm up when we come to a cold house with big rooms.  The next size down for that model is 18Kw.

Rollinghome

silvercar said:

Our hive controls when the heating and hot water are on or off. The actual temperature of the water in the rads/ water from the taps is controlled by the boiler. When the heating is scheduled on by the app, the hive room thermostats turn it off if the thermostat reaches the required temperature. 
You can have 6 on and offs each day, with different temperatures for each. So we have a slightly lower temperature in the early morning and early afternoon than we do late evening. Other times it is set very low for frost protection, but never reaches that low.

Advantages for us is the ability to switch the heating on or off when we are out and to turn the heating off when we are on holiday, knowing we can turn it on before we arrive home.

Thanks for that.  There doesn't seem much difference in cost between a Hive and a programmer + room-stat - provided it's reliable.