Advice re New Combi Boiler

ThemeOne

I am looking at a boiler replacement for a 2 bed flat with 6 radiators.

I had a local company quote for a Worcester Bosch 25i, although I realised afterwards they didn't test the water flow. I've done a rough test myself from the mains cold water tap in the kitchen and reckon it's about 12.5 litres per minute.

Looking at the recommended boiler's specs I see it has a flow rate of 9-10.2 depending on temperature. I've known others who've switched to a combi and find the flow of hot water is very poor, and am worried it would be like this if I went for this model.

Any thoughts or advice much appreciated.

Browntoa

Combi boilers suffer from hot water supply at adequate temperature and pressure if more than one tap is on at one time. probably not an issue in a 2 bed flat

If you have no loft above you then mega flow type hot water tank is not an option

daveyjp

OP you are correct. You need to match the boiler to the water flow. A 30i may be more suitable.

macman

You are comparing two different things. Cold water flow rate off the rising main, and hot water output from the boiler. The boiler has to heat the cold water to x degrees, so the 'hot' flow rate is always less than the cold flow, and lower still in cold weather.
There's no point in installing a combi that can heat the water faster than the rising main can supply it: the maximum flow is determined by the weakest link.
I wouldn't go near an RGI who didn't check your mains pressure and flow rate before recommending a boiler.

ThemeOne

macman wrote: »

You are comparing two different things. Cold water flow rate off the rising main, and hot water output from the boiler. The boiler has to heat the cold water to x degrees, so the 'hot' flow rate is always less than the cold flow, and lower still in cold weather.
There's no point in installing a combi that can heat the water faster than the rising main can supply it: the maximum flow is determined by the weakest link.
I wouldn't go near an RGI who didn't check your mains pressure and flow rate before recommending a boiler.

Thank you. So if I assume the flow in the boiler specs is the hot water output rather than the rising main input then the recommended boiler sounds like it’s about right. Have I understood correctly?

He should definitely have checked the flow rate though, I agree. I’m getting other quotes which will hopefully be more thorough.

daveyjp

With modern boilers there is no problem overspecifying for hot water. Ours is slightly overspecified. Mains was at 13l a minute, boiler can heat up to 15l.

It modulates the heat to ensure the water is heated to the temperature set by the user.