Help to understand quotes for new system boiler

[JackK]

Mainly up-front cost, including possible need for a bigger gas pipe to meet the pressure drop regs. Might be a little less efficient as it will be working at a big turndown.
Does it have to be a system boiler? A heat-only is easier to troubleshoot in event of a problem. It also allows the option of a F/E tank instead of an expansion vessel. There are pros and cons with each and opinion in the trade is divided, but my preference is F/E tank.

Why is a F&E preferred with corrsosion and oxygen able to enter the system

 

[Notch7]

but I'd like to understand the implications of having a boiler that's potentially too big. Can anyone please advise

A boiler that is too big might struggle to modulate down enough.

heating doesn’t need a lot of power in fact it’s a surprisingly small amount that is required to maintain a target temp,of 20 deg in a house.

 

[fixitflav]

Why is a F&E preferred with corrsosion and oxygen able to enter the system

The water in the F/E tank doesn't circulate through the system, I doubt whether corrosion is any different from using an expansion vessel.
With an F/E tank there's no need to check pressure and top up periodically, it looks after itself. F/E runs at lower pressure, so less likely to cause leaks (especially when retrofitting to an existing setup).

 

[mike42]

Might have been nice to give the quote (or approximate quote to stay anon) as always interesting to see such quotes and how they change over time.

 

[Murdoch77]

Has anyone checked the mains water dynamic flow rate to see if an unvented cylinder is feasible?

They both checked the water pressure from the outside tap and said it was OK. Is that what you mean? With our current system (header tank in the loft), the pressure downstairs is OK but it's not so good upstairs, especially in one of the bathrooms. We were under the impression that a new unvented cylinder would help with the pressure. Is that correct or not?

We have two bathrooms upstairs and two teenage daughters so we definitely want a system which gives us decent pressure and hot water for the showers.

 

[DP]

Unvented does give better pressure if mains pressure is upto scratch.
But cylinder hot water will run out. Having said that, recovery rate is fast.
Another plus is immersion heater. If boiler packs up, water can still be heated electrically- a dead combi means no hot water or heating

Just wife and I at home. 32kW Vaillant Ecotec Plus has served us faithfully with decent flow rate

 

[DP]

The water in the F/E tank doesn't circulate through the system, I doubt whether corrosion is any different from using an expansion vessel.

The surface area is open to air so will be subjected to ingress of air which EV is not
Rise and fall of water in F&E will also let air into the system water
This is one of the reasons why the feed pipe often blocks up with rusty plug of sediment.

A combi communicating pipe to EV will block up if flexible pipe used with black sediment
In 30 years not seen copper pipe blocked up similarly

 

[fixitflav]

The surface area is open to air so will be subjected to ingress of air which EV is not

But very little of it gets into the circulating water. F/E tank isn't subject to expansion vessel problems, which come up regularly on this forum.

Rise and fall of water in F&E will also let air into the system water

That was the case with open vent on the flow, cold feed on boiler return, but that went out 50 years ago. When it's plumbed boiler - open vent - cold feed pump level change is minuscule (or even combined cold feed and vent, which I'm not keen on, but some go for it).

This is one of the reasons why the feed pipe often blocks up with rusty plug of sediment.

Do you mean the pipe from the F/E tank to the system? Good reason to keep the inhibitor concentration up to scratch!

 

[Exedon]

See pic open vented on a H section did one last week even worse but that had a airjec fitted .

 

[Murdoch77]

So based on some of the advice on here, I've now got a third quote in and this time I asked for hot water priority. I'm sort of back to square one in not understanding the technical side of things and therefore not knowing which company to go with. This third quote is cheaper than the previous 2 (approx. £5k cheaper than the Worcester Bosch quote and £3k cheaper than the Vaillant EcoTec Plus 30kW quote). Is it missing something important or does it look OK? Thank you.

Draining down and removing the existing boiler, cylinder and tanks.
Removing all the radiators throughout the house.
Fitting a new Vaillant EcoTec plus 630 condensing system boiler in the airing cupboard with a vertical flue
Fitting a new Vaillant boiler protection kit (filter)
Fitting a new 250l indirect unvented hot water cylinder with all the valves, vessel and controls.
Rerouting the pipework to suit the new boiler.
Running a new suitably sized gas run from the gas meter to the new boiler position.
Fitting 8 new suitably sized radiators upstairs and 6 new suitably sized radiators downstairs.
All the new radiators will be fitted with new thermostatic radiator valves and lock shield valves.
The electrics will be fed from a 3 amp switched spur and a Honeywell T6 wireless programmable room thermostat will be fitted.
The system will be flushed, filled, tested and an inhibitor installed.
All internal and external brick and plasterwork will be made good and all rubbish removed from the site.
All work will be carried out to Gas Safe regulations and the boiler will be set up to the manufacturers instructions.
This boiler comes with a 10 year manufacturers warranty.

 

[Agile]

Officially the new rads should be sized to heat the house with a flow temperature of only 50 C all ready to use a heat pump in the future.

But as I said before the quotation should list each radiator size and make.

 

[fixitflav]

flow temperature of only 50 C all ready to use a heat pump in the future.

And to maximise condensation

 

[Murdoch77]

But as I said before the quotation should list each radiator size and make.

They all seem to have said the same thing in that they do a quick measurements initially to determine what's needed. They then do full calculations and list radiator sizes etc once you've accepted the quote so it's difficult to know which one to choose. I think they're all decent companies with good reviews, I just don't know which one to choose because I don't understand the technical details. I guess in simple terms we want the best boiler for efficient heating and easy access to hot water with decent water pressure.

Background: it’s an old house with 4 bedrooms and 2 bathrooms with tank-fed showers and fairly low water pressure. At the moment we have 17 radiators and 2 pre-teen daughters with long hair so having to switch the hot water on and then wait for an hour before having a shower can be a pain.