New Boiler

My plumber quoted £4K for a new boiler. British Gas are offering their seasonal discounts for about £3K.

Choice of Worcester Greenstar Ri 15kW - Regular or Vaillant ecoFIT pure

Any recommendations as to which might be better?

If the plumber is more expensive than British Gas then that is a bit concerning.

Although it is a while since I have priced a boiler install.

Cheers

Dave R

Not really. BG treat it as a loss leader and will try and scare you into buying their homecare, boiler services etc.

Note also that the trading name "British Gas" is used by several companies. the "British Gas" that installs your boiler is not the same as the "British Gas" that supplies your gas..

Personally I wouldn't touch BG with a barge pole of infinite length. I believe they trade on history, not current performance

Dave

Do you need a 15kW boiler? Has the heat loss for your house been determined by a competent person recently rather than salesman/plumber just assuming you need the equivalent of what is currently fitted.

See towards the end of

Last year I paid £3.2k (incl VAT) for a eco415 Vaillant (heat only)

BUT

This price included moving the location by 2.5 metres to an outside wall in an outhouse, changing the CH system from open vented to sealed pressurised. The price included all extra gas and water pipes, all components including a magnetic filter required for the 10 year guarantee), new flue, lagging of all new pipes, removal of a loft expansion tank and associated pipework and disposal of all removed items (old boiler etc.)

The work involved extending flow and return pipes through a brick wall

The price also included a power flush of the existing CH system. The job took approx 10 hours (A full day plus a short half day on the premises).

The boiler was wired into existing controls.

Local two man business, but only one person on site.

I thought the usual M.O. was to quote some crazy figure, and then give you a

Maybe they've been told not to do that, and have a different business model now?

For one thing, they're probably subbing out the job to some local fitter. Better to employ someone like that directly.

Theo

A great many years ago,I had a boiler installed by British Gas. Their contactor installed it wrongly (according to the instructions which he'd left behind. The error would make it use more gas. BG's inspector found no problem. I wonder why not?

I installed our next boiler myself.

WB Greenstar 15Ri ErP+ heat-only boiler installed a year ago. Some pipe work, filter fitted, new valve for F&E tank, boxing in. 11 hours work on Friday, 2-3 hours on Saturday. Total cost £1650. Local plumber/gas fitter of good reputation. Boiler is minimalist for controls (On-Off, temperature (analogue)). Error codes (not seen one yet) by blue flashing light. No probs so far.

The Worcester-Bosch customer controls are rubbish.

Oh indeed. You should first of all size the boiler to the worst case winter *total* heat loss of a fully occupied house.

And then add 50% to allow for fast winter warmup. Or even more if you have a lot of thermal mass inside the insulation.

Radiator sizing is based on worst case ROOM heatloss. As long as you had stats on the rads they will operate well below [peak output mostly

You size the boiler for the heat loss of your house. You then size the radiators to the heat loss of the room. If your existing radiators happen to be sized greater greater than the heat loss of room they can be throttled back with the lock shield valve or the newer generation of balancing valves. If the radiators are oversize you also have te option of reducing the flow temperature from the boiler which will put it into the most sufficient operating mode.

Why add 50%? For probably 95% of the days in the UK it will not be the worst case winter day and the peak boiler output will already be 50% above that required for a typical winters day. For the few really bad winter's days you may elect to leave the heating on longer or fire it up earlier.

I will admit that determining the heat loss could be a very good guestimate as the published u values for various walls/insulation/windows/floors may not exactly reflect your building but overall you could get within 10% of the real figure

Over sizing the boiler could mean that it isn't working fully in the most economic condensing mode or is short cycling for the majority of the heating season. Some boilers including one the OP is considering will only modulate 4:1.

The OP hasn't stated his house loss but if he is basing the new boiler output on his existing boiler and over the intervening years he has replace single glazing with double and increased insulation etc. a smaller output boiler may be appropriate.

Yes, radiator size is based on worst case room loss but also recommendation these days is to size radiators for lower flow temperatures and not the traditional output temperatures from gas boilers.

It is a wet finger estimate. If I want my UFH at say 19°C room temp and I start from 'i've been away for two weeks and switched it off' it takes about 24 hours to achieve it on a cold day.

Ther are TONNES of concrete and masonry inside the insulation that have to be heated up

If you live in a modern wood'n cardbaord over-insulated fart box, sure, you can get by with less.

Well mine is either on, or its off. And it doesn't take kindly to being on for 24 hours. That generally means it wont restart for several hours

It cant short cycle because the hysteresis on the thermostats is enough to ensure once its off its off for many minutes

I don't have heating on 24 hours a day.

Modern gas boilers may also have a timeout period to minimise short cycling. If the boiler has already modulated down to its lowest output and the flow has exceeded the boiler temperature setting the burner switches off and cannot fire up again for the very many minutes of timeout. Water is still circulating during this timeout period.

Short cycling on an older system may be more of a problem if the pump overrun is a short period and the boiler does not have a controlled inhibit timeout period. Not only does the boiler switch off but shortly afterwards the pump may also switch off, with the cycle maybe repeating every few minutes.

I cant avoid it if I want my UFH to warm up, because that's how long it takes

It is one of the reasons I am building my own heating controller right now, as commercial offerings don't have fine enough control over time and temperatures

Whatever. I dont have gas.

Short cycling is a result of bad system design. either the house needs heat or it doesn't. Ergo call for heat should be for many minutes duration at a minimum