Replacing Rayburn with Combi boiler

mrsdrudge

We have a gas powered Rayburn which was installed about 35 years ago, it powers central heating and hot water as well as the cooker.

Our house is a Victorian semi with four floors, and the hot water tank is on the third floor, with the bathroom and kitchen on the ground floor - so it takes quite some time for the hot water to get to the tap. The cold water and header tanks are at the top of the stairwell in the attic room, we are putting in a fireproof door and will have to raise the tanks into the loft.

Now considering installing a combi boiler and ordinary cooker in place of the rayburn. I know it is a thing of beauty but I just want the convenience of hot water on demand. The pump and associated central heating works are on their last legs and will need replacing soon in any case - they were in the house when we moved in 38 years ago, as were the majority of the radiators.

Anything else we could consider? We asked Octopus about a heat pump but it was agreed that in a single skin Victorian house this was probably not practical.

We are considering getting an interest only mortgage for house improvements - as have said - we have been here 38 years and the house is feeling it's age.

Albermarle

The immediate thing that comes to mind is that a combi boiler runs off mains water pressure, so there would be no need for the cold water or header tanks, or a hot water tank of course.

That would need some significant replumbing though, but is probably still the way to go. It would also mean that you would have mains pressure at all taps/showers etc. in the house and in the central heating. That would not affect the heating system as such, although it might mean you get a couple of leaks to begin with.

You need to check your water pressure. If it is too low ( the minimum allowed legally is still low), the combi will not work very well. If it is too high, it will need to be reduced.

Alternatively you could have a gas boiler, for the central heating and to heat the existing hot water tank, and leave the cold water and header tanks in the loft. This would be cheaper as less replumbing involved I would think.

mrsdrudge

I assume we'd need to get the water pressure tested before we start asking for quotes. How would we do this? Just ask any plumber? I know we'd need to pay a call out fee.

QrizB

Now considering installing a combi boiler and ordinary cooker in place of the rayburn. I know it is a thing of beauty but I just want the convenience of hot water on demand.

If you're fond of your Rayburn (and my mum loved hers, before she moved out of the old family home into a new-build) you could consider keeping it as an appliance to cook with but not using it for hot water.

Use a combi boiler (or a regular boiler, or even a heat pump) for hot water and heating.

gwynlas

With a four storey house you will probably need some kind of storage tank and pump to get sufficient power upstairs, we installed a megaflow system.

FreeBear

I switched from a Baxi back boiler to a combi a couple of years ago. Having a DHW tank in one of the bedrooms always meant having to wait for hot water from kitchen or bathroom taps. The tank was also poorly insulated which did nothing for heat retention.

The new boiler got installed in the hallway directly below the bathroom. Almost instant hot water up there, but still had a long wait in the kitchen. Location was a compromise based on where the flue could go, difficulty in routing of a 22mm gas pipe, and which taps had priority for hot water. Putting the boiler in the hallway had a small side benefit of waste heat from the casing adding to the heat generated by the radiator - Side note. There is some 6% of heat loss through the casing of most boilers. It makes sense to keep the boiler within the habitable envelope of the building rather than sticking it in the loft or garage. Same applies to any DHW tanks if you opt for a system boiler. Keep the DHW tank & boiler within the building.

A solid brick Victorian building can be fitted with a heat pump - The walls are likely to be 9" thick. Some of my walls are of a similar thickness.. Plenty of loft insulation and decent draught free windows & doors does wonders for heat retention.

If you stick with gas, it is well worth replacing the old radiators with modern larger ones - Do the heat loss calculations and oversize the radiators by 30-50%. This will enable you to run the boiler at a reduced flow temperature, pushing it well in to condensing mode and returning a higher efficiency. Side benefit is the radiators are cooler, thus reducing the risk of burns.

I run my Viessmann with a 40-50°C flow temperature and regularly hit 94% efficiency.

Albermarle

https://forums.moneysavingexpert.com/discussion/comment/82100573#Comment_82100573

I have never done it but if you google it recommends buying a water pressure meter. However you can get a feel for your pressure by measuring the flow rate. Which means measuring how long it takes to fill a container of known size and from that you can calculate the litres per minute.

Presumable local plumbers/heating engineers will have a good idea anyway of the water pressures in your local area. I think at this stage it is too early for quotes anyway. You need to sit down with them first and discuss the various options.

daveyjp

You need the flow (volume) measuring, not the pressure (force). Easy to do. Time how long it takes to fill a 2 litre jug from the cold water taps. 10 seconds is 12 litres a minute, good for a 35kw boiler.

However for a four storey house I'd ask a decent heating engineer to visit and provide a solution which meets the house design and location of hot water outlets.

knightstyle

Having grown up with a Rayburn, coal fired, I see where you are coming from. When a combi boiler was installed in our present house it was put in the airing cupboard in the place the hot water tank was. This is great as the kitchen is quite small. Couple of points though, if the hot water pipes are 22mm get them replaced with 15mm to speed up the time it takes for the hot water to get to the taps, plus make sure the installer is registered with the boiler maker and does everything required for the extended guarantee. Ours didn't so we had 5 years instead of 10 years!

Ectophile

There is a small risk that converting to a combi will reveal weaknesses in your plumbing. With a tank in the loft, the only pressure in the water pipes is from the weight of the water below the cold tank.

With a combi boiler, all the taps run at mains pressure. The central heating system is pressurised to about 1 bar when cold, and this could (but probably shouldn't) go as high as 3 bar with the heating running. If your plumbing is on its last legs, there's a possibility that a joint could fail somewhere.

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When measuring flow rate, make sure you use a cold tap that's at mains pressure, usually the kitchen tap. Don't use a tap that's fed off your cold water tank.

FreeBear

With a combi boiler, all the taps run at mains pressure. The central heating system is pressurised to about 1 bar when cold, and this could (but probably shouldn't) go as high as 3 bar with the heating running. If your plumbing is on its last legs, there's a possibility that a joint could fail somewhere.

Just had a quick look at the history of my boiler. Baseline pressure is around 1.3-1.4 Bar, increasing to 1.7-1.9 Bar when running. Did a hydraulic test of my system before the boiler was installed. Pumped it up to around 6 Bar, left it for a couple of days and the pressure held. Boiler fitted, and the system run at an inflated operating temperature (80°C in servicing mode), and a pin hole leak appeared in one tee joint. Easily fixed once the system had been partially drained.