New unsized boiler

Tallerdave

niktheguru said:

Why did you get a combi boiler for a 5 bedroom house!! Particularly if you cold water flow isn't great. Its a recipe for disaster. Surely this plumber should have advised you of the options. Did all the other quotes suggest a combi boiler?  Lets hope you don't want to use hot water in more than one room at any time!! Whilst its not forbidden to use a combi on a large house, you do lose water pressure if you use more than one tap with a combi, but you do have that advantage of instant hot water. For big houses system boilers are a better option.

In a 3 storey house with a combi I can't think of a more inappropriate word than "instant" for the availability of hot water! The benefit of a system boiler with a tank is that the tank position could be optimised to reduce the distance from the taps.

However, the OP's way out of this predicament may be to replace the ancient radiators, reflush, balance the system properly and possibly upgrade the pump to make the system a bit more responsive. 

MWT

Nickbo222 said:

The system was flushed prior to installation.

Flushed or just drained and refilled?

From the sound of things you already know the real answer though, and it is not going to be cheap replacing all those radiators with new ones appropriately sized for the rooms and the new boiler.

We went through a similar process, replacing 35 year old radiators, along with a boiler replacement (system boiler), and the amount of heat we now get from the radiators is very noticeably higher.

Cardew

Tallerdave said:

However, the OP's way out of this predicament may be to replace the ancient radiators, reflush, balance the system properly and possibly upgrade the pump to make the system a bit more responsive. 

This is the boiler. https://www.vaillant.co.uk/homeowners/products/ecotec-plus-combination-store-1152.html

I doubt it is possible to upgrade an integral pump.

I would be really surprised if 30kW is insufficient to heat the house.

Radiator balance/flushing and run at a hotter temperature should solve the problem, and of course getting an adequate water flow to the boiler.

That said I question the choice of any Combi for an older 5 bed 3 storey house.

Tallerdave

I agree a combi is insane but I loathe them from personal experience.  The place we're renting has an ecotec 637 37kW system boiler. 5 bedrooms plus massive kitchen extension with UFH. In the recent cold week when it dropped to -4 I think, it did struggle to keep the place warm when the UFH called for heat at the same time as the radiators - it's down to draughts.

That week we used 2100kWh of gas, compared to 1400-1600kWh in a typical winter week and 50kWh in summer (hot water only).