Which Type of Boiler / System?

[Deryck Tintagel]

I have been having problems with cold rads (https://www.diynot.com/diy/threads/number-of-cold-radiators.652613/#post-6150056) so have been getting quotes for a flush as nothing has cured the problem.

A couple of plumbers have suggested changing the boiler as the current one is 25 years old and we could get more problems once the system is flushed.

We currently have a conventional boiler with HW tank with immersion heater. The HW feeds one bath and one shower. It has been suggested that we can keep the HW tank as it is in good condition and convert to a pressurised system.

Woiuld a pressurised system give us any benefits?

 

[Mottie]

I’d say get your flow problem sorted first. If some rads are getting hot but not others, thar would rule out a faulty boiler in my mind.

When you say pressurised, do you mean the heating system or hot water (which is called unvented)?

 

[Harry Bloomfield]

Woiuld a pressurised system give us any benefits?

No real benefits, but a potential for more leaks due to extra pressure. The only real benefit, being both loft tanks will be no longer needed.

 

[dal5band]

It is possible to have a system boiler. You could call this a hybrid system. The system boiler is pressurised so the radiators are pressurised and the heating coil in the HW tank is pressurised. The CH small tank in the loft is no longer needed. But the HW side is not pressurised so still runs off the main storage tank. So this is not a combi system. Need someone with experience to confirm this. I agree there may be leaks on the radiators.

 

[Deryck Tintagel]

I’d say get your flow problem sorted first. If some rads are getting hot but not others, thar would rule out a faulty boiler in my mind.

When you say pressurised, do you mean the heating system or hot water (which is called unvented)?

That was my thinking to be honest. Get to a known good position before changing anything. A full clean should be part of the changeover, and this could uncover other issues but we deal with those if the arise. I think the boiler is OK - it runs and we get heat where the pipes are not blocked, just not is all areas


Yes, pressurised heating system, with gravity fed HW

 

[Deryck Tintagel]

It is possible to have a system boiler. You could call this a hybrid system. The system boiler is pressurised so the radiators are pressurised and the heating coil in the HW tank is pressurised. The CH small tank in the loft is no longer needed. But the HW side is not pressurised so still runs off the main storage tank. So this is not a combi system. Need someone with experience to confirm this. I agree there may be leaks on the radiators.

MIght be worth a think.

I briefly considered a combi, but we had a breakdown a few years ago and were left without heating for about 5 days. The immersion heater at least gave us hot water. Also, getting the HW from the combi boiler to the tank location to connect to the existing would mean considerable upheaval of floor sheets (not boards)

 

[stem]

The only real benefit, being both loft tanks will be no longer needed.

I have heard a couple of reports from people living in Kent that have been without water for days / weeks who now have heating now as their boiler pressure has dropped and they are unable to repressurise it from the mains. Water stored in a header tank in the loft would have prevented that.

Others who have water for a few hours at a time will also appreciate a 25 gallon cistern supplying their hot water cylinder as it will be topped up when water is available and can be used any time. Combis and unvented cylinders can only provide hot water when the mains supply is available.

On the other hand, anyone who has had a frozen pipe burst in their loft would be glad to see them gone forever.

 

[ericmark]

I had some cold radiators when I moved to this house. The reason was very simple, the heating had not run for long enough.

As each room heats up, the TRV in that room closes, and the water is pushed to rooms with the TRV still open. Theory is balancing the radiators with the lock shield valve, will result in all radiators having some hot water from a cold start, practice it is not that straight forward, worked A1 in mother's old house, but in this house, my attempts to balance have not worked that well. Mainly due to boiler not being a modulating type, but also down to using micro bore, I had a problem with kitchen radiator, intermittent sometimes OK but also sometimes cold, but also a problem unrelated to this, the hall cooled too slowly, so living room would get cold before the thermostat in hall had kicked in.

So I linked thermostats in the living room and wife's bedroom so they could start the boiler running, this in turn resulted in the boiler running longer, and the kitchen radiator now has no problem. Likely due to TRV heads closing the valves in some rooms, so more pressure for other rooms, but that is just guess work.

As to radiator cold at the bottom, question one is, does it matter? I reach behind me and feel the radiator and yes cold at bottom, but room up to temperature, so not that hot at the top either. Heat raises, so bottom will cool first. If the central heating is not running, then radiators will cool down, mine runs with a mark/space ratio, i.e. the boiler turns off/on, so radiators also get hot/cold depending on if boiler running and for how long.

Mother's house with a modulating boiler, the hotter the return water the cooler the boiler heated the flow water, so with all rooms nearly satisfied the radiators would only be just warm, that was not a fault, they only needed to be just warm.

 

[fixitflav]

We currently have a conventional boiler with HW tank with immersion heater. The HW feeds one bath and one shower. It has been suggested that we can keep the HW tank as it is in good condition and convert to a pressurised system.

You can't pressurise your existing HW cylinder. If you want mains-pressure HW it would need a different cylinder.
If you get a new boiler it could be a heat-only direct replacement, or you could have a pressurised type, with accumulator, and remove the F/E tank in the loft. But no advantage in going that route, and as others said, increased risk of leaks.

 

[ChrisJP]

A couple of plumbers have suggested changing the boiler as the current one is 25 years old and we could get more problems once the system is flushed

Plumbers quite often suggest replacing the boiler but, even though yours is 25 years old, if some radiators and you HW are getting hot then it is not the boiler at fault.
Probably need to start with removing the radiators that don't get hot and flushing them through with a hose. Then think about a power flush of the whole system. Then go round the radiators to balance them.
Only then consider a boiler replacement.
Personally I wouldn't go for any sort of pressurised system - as others have said there is an increased risk of leaks, and you lose the reservoir of water that the header tanks give you.