Heating System Upgrade (possible duplicate)

[Chris B]

I posted this a while ago but I cant see it on E-S apologies if this is a duplicate.

I am assisting with the recovery of an inherited property. The existing heating scheme was designed and installed by the (now deceased) owner in the mid 70s or early 80s.

It consists of a floor standing Potterton Diplomat with 2 water outlets one labelled DHW+Upstairs which is split to supply two separate pumps, the other labelled downstairs, with its own pump.

Timers/thermostats for upstairs and downstairs but no timer on DHW (Just a tank thermostat). And a relay box to ensure only two of the three pumps can run simultaneously. (or maybe its just to ensure upstairs and DWH don't run together)

No TRVs anywhere, obliviously.

Massive twin panel radiators (no fins) in every room, no obvious signs of corrosion on any of them (I would assume it has been regularly inhibited at least until the last 5 years or so)

The current water supply temperature from the boiler is 49C (this is clearly as designed as each pipe has a clip on thermostat with an arrow marked on the glass. The water temp is on the arrow.

The system certainly used to function as the house was always warm when visited - but I have no idea what the gas bills were.

From discussions with the owners brother he believed that large radiators at low temp was the most efficient way to run the heating.

That might well be true and it might well work if you are in the house all day but we have recently discovered that it takes 9 hours to bring the house up from 15C to 21C. (Outside temp 8-12C, the property has DG and Cavity wall insulation)

All the radiators are barely warm at the top and cold at the bottom.

So something has to be done in the short term but the house may be undergoing major upgrades in the intermediate future (Showers fitted , possibly en suite etc) but the exact detail/layout of all this is still TBD.

The new owners are considering a modern boiler, I think as much for safety reasons as any other as they don't trust this huge great lump in the kitchen not to be leaking noxious gasses, (a CO monitor has been fitted as a temporary measure) and the chances of getting anyone to service it are pretty close to zero.

So my questions are.

1) I am planning to remove all the radiators take them outside and give them a good hosing through. Would this leave sludge in the pipes and if so how can it be removed prior to fitting a new boiler. Would this be adequate or with radiators of this age should they be replaced along with the boiler?

2) Would the system described above be suitable for adding a modern boiler pretty much one for one swap with the existing (having flushed out all of the radiators and fitted TRVs) or would major changes be necessary. I have looked at the DIY WIKI and it states that with modern TRVs oversized radiators are not a problem.

3) If a modern boiler is fitted this winter are they all suitable for using with a pressurised water cylinder if that is the route taken in a year or so when other modernisation work is done? The Worcester Bosh website seems to state that their regular Greenstar boilers are compatible with gravity HW or their own Greenstore (pressurised) cylinder.

Any helpful advice appreciated.

[Graeme]

In message , Chris B writes

I cannot add anything particularly useful to most of your points except to say that our ex shop, which is now my play room (!) had huge old non finned single panel radiators which were installed 1979. They worked, but no TRVs, which was a nuisance, so when fitting TRVs the rads were replaced with modern twin panel finned versions. The difference in controllability and heat output is amazing. Bottom line, the new rads are shorter than the old, yet give out far more heat.

[Capitol]

The boiler can be serviced, just about all parts are available. Up to the point where the heat exchanger springs a leak, these units will go on for many years. A modern boiler has a life of 7 years before replacement.(gas fitter experience)

I'd change the radiators for modern twin panel finned units and fit TRVs.

[Rob Morley]

Simple physics says it's not.

You could just try turning the stats up and see what happens (the rad valves might need adjusting too to get even heating from each one).

[John Rumm]

They might be triggering the DHW pump direct from the stat.

That would limit the maximum DHW temperature to under 49 deg as well... (not good from a sanitary point of view)

With a modern condensing boiler that might be true, for for an old cast iron lump it just seems like a way of ensuring accelerated corrosion of the main HX due to condensation of the flue gasses.

That sounds like either a insufficient flow problem (check the pumps), or a serious sludging up problem.

Checking the pumps and doing a mains pressure flush as a short term fix:

It should be fairly simple to service I would have thought... check the combustion, sweep out the HE, etc.

If having flushed each rad, you do a final flush through the whole system, that should be adequate. You can dump some system cleaner in a week before doing the flush.

Over sized rads (in therms of performance rather than physical size necessarily) are fine on a modern modulating condenser - it can run lower flow temps for greater condensing efficiency.

Yup, from the CH / boiler point of view a unvented cylinder looks pretty much the same as a fast recovery conventional cylinder.

Yup, and will also be compatible with any other make of unvented cylinder as well.

You may need to look at a boiler that is capable of split temperature operation so that you can run low flow temps on the rads, but still have higher temps for a cylinder recharge. Its more normal to run the DHW separately from the heating so that you don't heat the rads to DHW temps or vice versa.

A single pump and S Plan+ type system may suit the setup best. You could look at a system boiler if you want less "clutter" in the system.

If its a larger house then consider weather compensating controls with an external stat as well. That will allow the system to run cooler for most of the year, but then automatically ramp up the flow temperature when required on colder days.