New central heating - what should I be asking for? | Central Heating Forum | Plumbers Forums

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We live in a 1980s four-bedroom detached house. The time has come for new central heating.

The current system is a mild revision of the original heating installed when the house was built, and this revision was largely to replace a life-expired boiler:
  • non-condensing fan flue boiler
  • open vented
  • vented hot water tank in an upstairs airing cupboard
  • TRVs on half the radiators
  • no bypass in the heating circuit
  • Y plan
  • basic controls - bimetallic room thermostat, bimetallic hot water thermostat, 7-day timer
The current boiler is still safe (inspected last month) but is obsolete with no parts available. The system is horribly inefficient and the heating does not hold a constant temperature. I'm fed up with the microswitch in the three-way valve actuator failing (Honeywell, then it was changed to a Danfoss valve).

It is time for a new system. We want to reuse the existing radiators and heating circuit, as we cannot face the disruption needed to replace them. We are still a couple of years away from replacing the existing double glazing with windows with heat-reflecting glass and we still have more work to do on insulation. For all those reasons, an air-source heat pump is not an option, so it will be a case of powerflushing the system and fitting a new natural gas boiler. However, I am willing to replace everything else if it makes sense to do so.

The design and installation of a new system is, of course, a job for a professional. However, I want to be an informed consumer, hence this post.

It seems that the biggest choice is what to do with hot water. We have a large jacuzzi in one bathroom and a pumped mixer shower in the second bathroom, so I suspect that a hot water tank makes more sense than a combi. If we stay with a tank, priority domestic hot water seems to be the way ahead, so I presume that will mean a new tank with a bigger coil and perhaps a smaller capacity (the current tank seems too large despite the current bathrooms). PDHW will have the advantage of getting rid of the three-way valve with its failure-prone microswitch. If we are replacing the tank anyway, does it make sense to go unvented to give us greater hot water pressure?

So far as the radiators go, I'm not especially keen on pressurising an old circuit which has been unpressurised for the last 42 years. I do not care about the space used by the header tank, which is in a corner of the loft out of the way. Is the best option to stay open-vented, or would it be better to have a system boiler and pressurise the radiators?

I want every radiator on a TRV, so a bypass is needed. Whilst the system is being upgraded, is it best to replace the existing TRV bases or is it acceptable to leave them until they jam or leak?

I want smart controls that will modulate the boiler properly, as well as a boiler that will do dual temperatures for PDHW. I'd rather have OpenTherm on the boiler so that I have flexibility in which controls to use. I have looked at Evohome, though maybe there is a better alternative.

Is fitting a magnetic filter worthwhile, or is this just an expensive upsell for a limited extra warranty on the boiler?

I would welcome recommendations for boiler brands and for contractors willing to do this job in Bedfordshire. I am not interested in someone who is going to tell me to put a new boiler into the current flawed system rather than redesign the system properly using modern principles.
 
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I recommend that you spend you efforts on finding a good local independent heating engineer and then get them recommend a system. Tell them what your priorities as a user are (budget, future running costs, space, controls) and let them get on with it. Ask questions about their proposed solution(s) but don't be the "I've got an engineering degree and think I know more about your trade than you do." customer or you might have WAT [*] added to your quote.

This:

"I'm not especially keen on pressurising an old circuit"

is a common prejudice but in my opinion it is wrong. The pressures involved will not cause leaks, the sealed system just makes them more obvious so they can be fixed in a timely manner when they do occur.
 
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The return on investment of heat reflecting glass is way less than a properly designed heating system. Larger radiators (modern doubles) will probably be a straight swap for your existing probably corroded radiators, allowing lower flow temps from the boiler so even higher boiler efficiency. Pressures are not significantly higher and corrosion much less with a sealed system. An unvented hot water tank could also be heat pump ready and get those tanks out of the loft. If you're that worried pressure test your existing setup. A heating engineer could design the system to at least be 'heat pump ready'.
 
I recommend that you spend you efforts on finding a good local independent heating engineer and then get them recommend a system. Tell them what your priorities as a user are (budget, future running costs, space, controls) and let them get on with it. Ask questions about their proposed solution(s) but don't be the "I've got an engineering degree and think I know more about your trade than you do." customer or you might have WAT [*] added to your quote.
I am trying to understand enough to get a feel for what I should be hearing from the right person for the job, not to do their job for them. System design and product selection is a task for the professional!

I am aware of the shortcomings of what we currently have and acknowledge that I am looking for a total system redesign.
 
Who is controlling this forum?

Why would anyone deride a person who comes to this forum, requesting information for a job on their house, that is not being unreasonable?

All this person is doing is asking questions about a new heating / hot water installation.

The OP has obviously done some research and wants some of their ideas clarified and suggestions if they are on the wrong track.

Are any of the questions asked different to any questions asked by customers who have done their own research into a system they want installed?

FWIW - If I was in the UK, I would be knocking on his door to do the job.
 
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I am trying to understand enough to get a feel for what I should be hearing from the right person for the job, not to do their job for them. System design and product selection is a task for the professional!

I am aware of the shortcomings of what we currently have and acknowledge that I am looking for a total system redesign.
It's difficult to advise without seeing the system and getting a good idea of what you want.

It's a good idea to future-proof but it could be done in different stages. Just make sure that whatever your putting in is up to future spec.

Most boilers aren't setup for HW priority (with dual flow temps) and its a fairly niche install.
I think Intergas, ideal & Vaillant have options tho.
(I've just completed one with a Worcester 4000 but I can't reccomend it as not technically allowed).

I think the point that was being made before is that your probably better off with a good reliable local engineer than with (what some may consider) an over complicated installation.

I guess the question is how much do you want to spend?

Yes a system boiler with a high gain (dual coil) UV HW cylinder, resized rads for 50°C flow temps, HW priority and load/weather compensation would be ideal (also zoning/smart TRVs may be an option)!
But they can also all be done independently without any issue...

Regarding pressurising your system, I think your best taking advice from your engineer but it would have to be a particularly ropey system for it to be an issue. As said the pressures aren't very high.
 
Also for arguments sake-
Just a straight swap for a regular condensing boiler would prob give you 90% of what you want and leave you plenty of time and money to invest in a whole new renewable system when the time comes.

Renewable installers have the niche things down and your little regular boiler could make a really usefull gas backup if you decide to go all in within the next few years🤷‍♂️
 
If you’ve got the space and cash, bin the lot and modernise it.

New system boiler.
Low loss header.
Mains pressure tank in tank hot water cylinder/s, full recovery in close to 30 mins.
Kill the cold water storage tank and install a dab 400 litre booster pump/tank.
Can wire it however you want/with what ever controls you want.

This is obviously a bit overkill for your property but here’s a recent one.

Even tiled the floor.

E57ADEA9-23C4-497B-830D-70D62DE5A73E.jpeg
06DAD010-24DD-4508-A4FB-8362BECB1A66.jpeg
1529D152-198F-4430-B7A9-22F5655E9973.jpeg
E5A92630-DF80-404F-925B-66A7B6654405.jpeg
F09FA4B8-273C-4407-AE2B-9FD45BEBCDDE.jpeg
477A2278-AA18-421C-8ACB-E657392375B0.jpeg
 

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