How to replace a Worcester Hi Flow with something similar?

[a.john]

My first post. I'm not a plumber etc but do have some understanding of how these things work.

Our Worcester Hi Flow is getting rather long in the tooth. It should have been replaced but still works pretty well really but will be replaced some time early next year.

Since Bosch took over they aren't available any more. Not gas anyway. It's a boiler with a built in heat store. General idea is that a bath can be run which will deplete the heat store but another can be run 4 min later. It does this by using the same type of gas valve as a combi so there are 2 rates of heat output and ch and hot water temperature can be set separately. It's also a vented system. The water still runs warmish when the heat store has been depleted because the store is so small. The heat loss from it is amazingly low.

It's an old house with solid floors so I would prefer to retain a vented system and also avoid a system boiler.

I've spent some time looking at boiler installation manuals to see if this sort of system can be replaced. There is no problem finding conventional boilers or heat stores but I can't see any signs of a way of getting separate central heating and hot water store temperatures and wonder if this is possible on all or any of the ones that are available. There doesn't seem to be any problem wiring them up for 2 thermostats. One has connections built in for that but it's a vented system boiler. What I don't want to have is a set up where an immersion heater needs to be turned on if the central heating happens to be running at too low a temperature. We have enough radiator to avoid running them at max temperature.

We have 2 bathrooms and several bedroom sinks. I don't think a combi would work out. The ancient tanks were taken out a very long time ago and when we moved in the house was fitted with 2 very old instant gas water heaters and economy 7 -heating the place when we were at work.

:smile: Hope some one can help. I rambled on about the Worcester as they haven't been around for some time now and people might not have seen or even heard of them.

John
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[Chalked]

Hi
A high flow is a combi. It's a storage combi. It has a small tank that stores heating water at high temperature. When a tap is opened, it pumps this water through a plate heat exchanger that transfers the heat to msins water, thus heating it.
After a while the store is depleted and water cools. But given a short time it will catch up.

There are some storage combi boilers about. Vaillant make a wall hung one that is a beast of a boiler.
A lot depends on your water main pressure and flow. Thus will determine what is possible. I would get your gas safe engineer to specify a system boiler and a pressurised cylider.

 

[joni os]

Should be possible to locate unvented cylinder in same position as Highflow with boiler close by. This will utilise existing pipework. Regular boiler on S plan will suffice. Some taps/showers, if installed post Highflow, might require 0.5bar minimum, so unvented system necessary.

 

[Last Plumber]

Bang on chalked
100% agree.
Vaillant 937 (837 with storage vessels)
I think best bet, System boiler and Unvented

 

[a.john]

Thanks for the replies. I will look at the Valiant. My thoughts were heat store or unvented tank where the hi flow is and probably boiler in an airing cupboard that's very close by. That way all of the pipes are there. I still prefer the idea of a heat store over an unvented tank though. What surprises me is that none of the conventional boilers seem to have the ability to have 2 set temperatures. It;s an old problem. I remember having to switch the immersion heater on 1//2 hour before having a bath when I lived with my parents. Lots of people did.

I've noticed that the thing that needs replacing most often on a boiler is the pump. Years true. So I would prefer it not to be a system boiler to keep the cost of those down. The other aspect is I suspect we will have problems with a sealed boiler and finish up needing extra expansion vessels due to the pipework. We have a solid ground floor so boiler etc is on the 2nd floor. Most of the pipework is well hidden and needs to remain like that.

The Worcester doesn't maintain the water temperature when the heat store is used up. The water is never cold but drops to a level that wouldn't be hot enough for a bath. Worcester do combi's that have some sort of instant hot water idea that I think is electric built in but having tried it in some ones house it's hopeless. That's the reason I prefer a real heat store. It wastes a bit due to heat loss out of the pipe work but on the other hand if some one washes their hands they needn't wait for the water to warm up or get rather cold hands. I'm convinced the win out when a bowel is filled for washing up too especially as hot as my wife has it. I'd guess this is why they were popular in places that used lots of hot water - pubs, businesses etc.

John
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[Tonycane]

The greenstar 440 cdi is still available, decent boiler but condense pumps seem to only last about 5 years. No experience with the vailliant but heard there pretty good.

 

[Gasmk1]

also vailant 111 or 222

 

[Gasmk1]

also viessmann 111 or 222

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[a.john]

The greenstar 440 cdi is still available, decent boiler but condense pumps seem to only last about 5 years. No experience with the vailliant but heard there pretty good.

An option. I had more or less dismissed those as they are only for a sealed system now and wondered if they if they were just a combi in box. However it might be possible to fit any extra expansion vessels in the airing cupboard if needed. The piping goes that way and the only thing between is a partition wall. I'd probably go for the 550 now even though the lower power version of the old one has been ok. The heating output looks to be more or less the same on the new ones and more than we need. Just more going to water that only gets used if needed.

They do mention the case when the boiler is on a vented system but give no details of what head it needs. I might phone them up and ask about that but going on Ariston their tech help wasn't much good. I'd have had hot water at ch temperature. I had a yes it will do that with one of their conventional boilers. There doesn't seem to be any way of setting a different hw temperature in the manual.

:wink5: Afraid I spec'd the set up we have. At the time I had a number of plumbers in and wasn't too happy about what they said. The only people who did heat loss calcs were the gas people. I'd left mine out by mistake and the man from the gas came up with the same number. I did all of the radiator pipe work myself due to the problems with the house and then got some one in to finish off and install the boiler. I just did the pipe runs to the radiators and left the main runs and connecting them up to the plumber.

:devil2: Looks like I had better check the price of a condenser pump and see if a maintenance contract would be worth while. They have moved the circulation pump to the bottom. The old ones had it at the top and I suspect that the extra heat reduces their life.

Only problem from my point of view is that some one else's boiler and a separate heat store would probably work out cheaper. So if any one does know of a boiler that can set separate hw and ch temperatures even via add ons I'm still interested but no combi's.

John
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[joni os]

Viessmann on 4 pipe system with unvented cylinder, worthy of your consideration.