Combi boiler

mollie78

Hello, I've posted this elsewhere on the internet but looking to get as many opinions as possible.

We have a 10 year old Vaillant system boiler and a 30 year old hot water cylinder. Boiler needs replacing and, since we don’t currently get enough hot water for our needs and could really do with the space where the cylinder is, we are toying with getting a combi. House situation is 4 bed, one bath with shower over, but would like to future proof in case we add an en suite. Main requirement is to maintain a powerful shower (currently have a power shower which gives around 15l per minute, mains pressure tested at 20l per minute). Power shower will be replaced with a digital shower - no rainfall head if that makes a difference.

Various plumbers have recommended the following boilers - Veissmann 100w 35k, Veissmann 111w 35k storage boiler, atag ic39. We want good but not overkill. Can I ask for thoughts? I’m happy to hear ‘stick with a system boiler and get a bigger cylinder’ if that really is the best option. Thank you.

Lorian

What's wrong with the current boiler and what model is it?

bris

If you want a 15l PM shower then a combi isn't going to deliver that.


But you would get by with a decent combi with what you currently have.


If you do decide to add an En suite and find you have more demands for hot water then just change to an unvented system.

tacpot12

A combi boiler isn't going to meet your need for 15l/m without being significantly oversized compared to your heating needs.

A system boiler is the best solution for you. What you seem to need is a bigger cylinder, and space where the current cylinder is, so I would look to invest in a larger cylinder in a new location. If you live in a house, there will be somewhere in the loft that a bigger cylinder can be sited. You can get horizontal cylinders if the vertical height available is an issue. If you get a new cylinder, specify one with 50mm of insulation. Most plumbers will supply one with 35mm of insulation as they are not the ones paying the heating bills!

I am surprised that a 10 Year old Vaillant system boiler needs replacing already. Have Vaillant looked at it? If not, I would call them out. I had a Vaillant combi boiler condemmed as a being beyond economic repair by a local boiler engineer, but Vaillant only charged £300 to repair it. Much cheaper than the £2000 quote for a new boiler!

mollie78

Thank you all, I'll explore the bigger cylinder in the loft option, it does sound like it would solve our needs as in all other ways the system set up works well for us.

mollie78

Just to add to this, there was a mistake in my original post, when I said the boiler needs replacing I meant the cylinder needs replacing (we've had various issues with it plus as I said we don't get enough hot water from it). So our original thinking was get a combi instead, therefore gain the space where cylinder is and get more hot water. But if we look at replacing the cylinder instead as advised, should it be a vented one as we currently have or should we look to swap to unvented (or is this a massive job)? Current set up is vaillant ecotec plus 630, hot water cylinder in airing cupboard, cold water tank in loft, power shower. Thanks again for any advice you can give, all the plumbers we've seen so far have all suggested the combi route but I'm keen to understand this alternative.

vw100

The newer combi boilers now can handle more demanding hot water requirements better than say 5 years ago. The combi needs to be specified right and other factors need to be considered such as pipework quality, - by that I mean the routes the water will take and also the pipe sizes running under the floorboards. Mains pressure and flow rates is an important one to measure if going for a combi setup. You can get storage combi boilers which have a mini tank at the back making them bulkier in size which can handle higher DHW demands than normal combi's. Valiant and Viessmann boilers are two that come straight to mind that have this option and I am sure there a few others now on the market. if you opt for a combi factor in a upgrade to 22mm gas pipe if you currently have a 15mm pipe. Some may even suggest 28mm for the heavy duty boilers.
Your other option is a unvented cylinder with megaflow - it will be a system boiler with a pressurised tank and it will give you 'unlimited' hot water (until it runs out, tank size dependent). Most larger houses have this setup, however now with better combi boilers, some have gone over to the combi route.

mollie78

Thank you vw100. We have had a quote for a viessmann storage combi, which we do have room for where the current boiler is. Can you explain the benefits of an unvented system over a combi please? I've been looking at the horizontal tanks which we could site in the loft, and then keep the system boiler (assuming it is possible / plausible to swap from a gravity fed system to an unvented cylinder)?

SuzieSue

mollie78 wrote: »

Thank you vw100. We have had a quote for a viessmann storage combi, which we do have room for where the current boiler is. Can you explain the benefits of an unvented system over a combi please? I've been looking at the horizontal tanks which we could site in the loft, and then keep the system boiler (assuming it is possible / plausible to swap from a gravity fed system to an unvented cylinder)?

The Viessmann storage combi won't have an immersion heater. The unvented cylinder probably will, so if your boiler breaks down you will still have hot water.

The storage combi should be cheaper than a separate boiler and unvented cylinder.

Not all heating engineers can work on a unvented cylinder.

vw100

The advantage of a system boiler with a pressurised cylinder is that it can cope with higher water demands. Basically the cylinder, megaflow type of tank will store hot water which is ready and will feed multiple showers/baths until it runs out. The tank will have a immersion coil which can be flicked on with a switch or the system boiler will feed it hot water for storage. This setup is a known setup for households with higher hot water demands and you can run things like power showers. Also if the boiler breaks down you still have access to hot water via the cylinder but not central heating.

The more common storage combi boiler's come with approx 50 litre tank, (a power shower or bath will drain it quickly) which once runs out the boiler will run as a normal combi.

Installing either system will involve a fair amount of work with alteration of pipes and the disconnection of tanks in the loft. Yes it is possible to convert from a vented to a unvented system or a combi. Also with a unvented system it supposed to be annually serviced as the cylinder is under high pressure.

Your installer should specify the correct system factoring in everything in the house. With a gravity system you have you may have a regular boiler rather than a system boiler.