Replacement boiler - do radiators need replacing too?

Working_in_pyjamas

I have a very old combi boiler that's on it's last legs, I'm looking to get it replaced and also have a new shower fitted that is connected to the boiler (to replace the current electric shower).

Whilst I'm having the work done is there anything I'd 'need' to have done at the same time? Do radiators need replacing at the same time? The house is around 35 years old but I've no idea how to age a radiator. The boiler appears to have been replaced at some point in those 35 years as there is a cupboard where a hot water cylinder would have been, but it looks ancient and is totally obsolete and I'd guess it's 20 years+

Thanks in advance for any input

bris

If the radiators are old style then doing it now would be beneficial in the long run if it isn't costing to much. You don't however need to replace them if you want to save a few quid.  

Working_in_pyjamas

bris said:

If the radiators are old style then doing it now would be beneficial in the long run if it isn't costing to much. You don't however need to replace them if you want to save a few quid.  

Thanks, ideally I'd not replace them just yet - I looked at Boxt quickly (will be using a local independant) to get a rough idea of price and new radiators would be an extra £1500 which I'd rather not spend if it can be avoided.

theoretica

If you decide against changing them it may well be worth getting them cleaned out of gunk.  Do they have individual thermostat valves?

Working_in_pyjamas

theoretica said:

If you decide against changing them it may well be worth getting them cleaned out of gunk.  Do they have individual thermostat valves?

Is that the same as a power flush? I'd read that a power flush is needed when fitting a new boiler so was planning on having that done.

They do have individual thermostatic valves but they're plastic and quite yellowed with age! I don't ever adjust the temperatures as I have a Nest so the valve in the room with the Nest thermostat is on full blast, radiotors in rooms that aren't used are on low and rooms that are used are on medium.

Jeepers_Creepers

Hi WiP.

Do you need to replace the rads as well? No, not as long as (a) they are solid (little internal rust) and (b) are not full of sludge.

There are two main issues I am aware of when swapping from an older 'conventional' vented boiler to a 'sealed' pressurised type:

One is that the new one will now be running with your pipework at around 1 bar pressure, whereas the old system just had the weight of the water in the header tank in the loft to cause it concern - ie around 0.3bar. What difference does this make? It shouldn't make any, but if your pipe joints are weak or corroded, or if a radiator is badly rusted internally, then the extra pressure could give you leaks or worse. Usually, tho', provided the plumber is happy with the condition of your existing system, you should be fine.

The other issue is that your pipework and rads will almost certainly have some black oxide 'sludge' coating them and sitting along the bottoms of the rads. 'Old' boilers with large waterways inside didn't find this a problem, but modern high-efficiency boilers - especially combis - transfer heat quickly by having lots of narrow waterways inside, and these can - often are - blocked by sludge. So, you either need to ensure that the sludge is cleaned out, or else you may need to swap the rads and ensure there's no sludge in the pipes.

This cleaning is a standard part of a new boiler install - it's often referred to as a 'powerflush'. In addition, they should fit a magnetic filter in the pipework to catch any remaining sludge, but this isn't a guarantee either.

Are you capable of some plumbing DIY?! Can you remove a rad? If so, do so and see what comes out when you tip it on its side. Flush through well with a hose and see if more 'black stuff' comes out. Bear in mind that running cold water through it will not shift all the well-adhered sludge.

What you could do is to give the cleaning a good head-start. First try and ascertain if - how much - sludge there is by removing one rad (on a downstairs circuit if you are multi-storey). When you refit it, add a really good dose of powerful system cleaner like Sentinel X400. Chuck one or two bottles in and run your CH as normal, making sure every rad is nicely open to allow a good flow through each. After a good few weeks, drain down and allow the header tank to flush it through - you may need to refill with water, run the CH and then drain again.

Or, leave it all to the plumber - he'll use a machine.

As always, call out 2 or 3 plumbers for quotes and also to discuss the job. Listen to what they say, and also how well they listen to you. If you do need to replace some rads, then - especially if they are in the reception areas (where you'll want most warmth) - consider fitting a size up from what you had, or increase the output by going from, say, single panel to double, or ones with extra 'fins'. You'll then be able to run your new high-eff boiler at a lower temp but still get the same heat out as before = less stress on the boiler + energy savings. 

Working_in_pyjamas

@Jeepers_Creepers

Thank you for such a detailed reply, really  appreciate it. My old boiler is a combi boiler, does that make a difference when you’re talking about vented V sealed and the pressure etc?

Unfortunately I’m definitely not capable of any DIY plumbing to try and clean them so would definitely have to leave that to the plumber. I’d planned for the system to have a power flush but changing the radiators is an added expense I could really do without.

Jeepers_Creepers

Ah, so your current boiler is also sealed - it has a pressure gauge on it? In that case the 'pressure' bit won't apply.

Old - non-condensing - combis do have wider waterways, tho', so are less prone to blocking up, so a 'clean' is an essential part of any new install (and the fitter will need to do this to fully conform and activate any warranty). 

Good chance your rads will be fine. Do consider fitting new TRVs and lockshield valves tho' - around £20 a set for a quality make like Pegler :-)

Working_in_pyjamas

@Jeepers_Creepers

Yep, it had a pressure gauge - I occasionally need to top it up, but not by much and not very often.

Do I need to fit new TRV’s If the radiators already have them? 

Jeepers_Creepers

TRVs will be controlling all the rads away from the room which has the 'Nest', and they tend to start going wrong (sticky, not responsive) after around 10 years.

So, yes :-)  (Well, you don't need to - but you should...)

How often do you need to top up your system? What does the pressure fall by each time? (Every time you 'top up', you are diluting the 'inhibitor' chemicals in your system, and potentially allowing it to start corroding...)

Working_in_pyjamas

Jeepers_Creepers said:

TRVs will be controlling all the rads away from the room which has the 'Nest', and they tend to start going wrong (sticky, not responsive) after around 10 years.

So, yes :-)  (Well, you don't need to - but you should...)

How often do you need to top up your system? What does the pressure fall by each time? (Every time you 'top up', you are diluting the 'inhibitor' chemicals in your system, and potentially allowing it to start corroding...)

Thanks, I can stretch to TRV’s but radiators too would hurt!

Ive probably topped it up every 4 months or so, today it was around 0.5 so I topped it up to 1 - literally 2 or 3 seconds of water. I didn’t realise about diluting what was in the system!

Thanks to everybody’s help I now know what I need to be asking for quote-wise so can get a couple of quotes and hopefully get it done fairly soon.