Plumbing (Boiler/Valves) Help

Sounds to me that the OP has a semi-commercial system and that the boiler is severely undersized amongst other issues.

Twenty nine ‘old school rads’ three zones a hot water cylinder and a boiler with an output of 38kw doesn’t, on the face of it, sound good to me.

 

Certainly made me wonder how much insulation the house has. We're a 4 bed house with seven rads and 19kW. The bedroom rads hardly ever output much as he heat percolates from downstairs.

Only used the open fire once this winter as there's a nest in the chimney and the sweep's wary of Covid.

 

If there have been problems from the start then gradual sludging and/or scaling is less clear as a cause of the problems but when did you last flush the system and add new inhibitor?

The pump speed setting will determine the flow/head point where it operates. CH pump speed is normally set, AIUI, to the minimum speed where all zones receive good flow. That seems to be one of your problems hence an issue to check out.

Then, I was looking for a potential cause of leakage other than bad valves. Since you write that they have already been replaced without impact on the problem.

A fault where the pump overruns for a short while post-burn as normal [1] but against a completely closed system will cause pressure to rise towards the maximum the pump will generate. Unless there's a working means to handle that (e.g. a bypass valve - but there are other means too), that might force flow past closed valves. I am not sure, however, if this is a real issue or not without knowing the system and testing it.

If you don't have the knowledge or means to test possibilities yourself, it's definitely worth asking your plumber if he/she knows any possible causes of your zone leakage problem other than poor zone valves. And the poor flow to your upper floor. My experience is limited but possibly enough to ask an expert a pertinent question in amongst nonsense.

And by "overspill" do you mean hot water flowing out of a vent pipe into a header tank? AKA pumping over (assuming the system is open-vented - not sealed). Pump-over might also be caused by excess pressure but also happens from bad plumbing - the cold flow, the vent pipe and the pump in the wrong juxtaposition. And if that's a problem you have, an installer might have set the pump speed lower than optimum to reduce pump-over.

If this were my system I would be checking, and hopefully eliminating, the above to try and get to the root causes.

[1] Commonly used to protect a boiler's heat exchanger from transient overheating when flow stops at the same time as firing stops.

 

Could be a long shot but is it possible a pump has been replaced and new one put in the wrong way round?

Might explain weak valve shut and overspill. Also check output, mine's set on 3m constant head but your flow sounds a bit low so maybe try double that.

I never use a 15mm pipe when 28mm will do!

 

Thanks again for all the input. So I have some people coming this week to look into things further, I'll consolidate the thoughts on the thread and see what they say.

The 29 rads is a bit misleading, I really doubt if we ever need more than 12-14 on in the house. When the house was renovated, the builder put one under each window and some rooms got extras too. I think it was totally over the top on reflection. The house has new double-glazed sash windows throughout (we did that before the house was listed) and has interior insulation as well, plus loft too. So I think we are good on those fronts at least.

 

Aye but it’s a lot of water regardless of rads being turned off which isn’t great to be honest cause the rads corrode (all rads corrode) and then they sludge up plus the valves stop working and last but not least the pump ‘forgets’ those rads.

Twenty nine rads is mental I have 15 K2 type rads in 1936 brick built detached three bedroom one bathroom & one shower room bungalow and a 35kw combi with the heating range rated to about 18kw all of the rads except two have TRVs and all of the rads are turned on.

 

Yes, well if I quote a classic Irish phrase, it's a case of "well I wouldn't start from here if I were you"....trying to make the best of it - we plan to be in the house for maybe 10 more years, we'll do it *much* better next time!

 

What you really need to do here is to do a heat loss calc there's plenty of calculators on line and I'm positive that you'll be amazed at how much heat you actually need to heat the house those 'old school rads' have huge amounts of water in them and huge amounts of water equates to huge fuel bills.

I've no idea of what your requirements are heat wise and no idea what type of house you have but Dublin isn't much different from Glasgow vis weather and temp but if you don't need all of those rads once you've worked out how much heat you need then get rid of the rads that you don't need.

Twenty nine rads is at least 29kw load and probably an awful lot more, the cylinder is about 3.5kw but you don't include that output now when designing a heating system and back in the day you used to add on 10% on top which you don't have to do now but we're getting very close to your boiler output of 38 kw heat output an ordinary 6mt head pump will struggle with that load.

 

Thanks for this: I'll look to see if we can permanently disconnect some of the rads when the people come.

 

I hate rads under windows with long curtains.

Been here 30 years and get rid of one every so often; we sometimes move them to the side or refit tall narrow rads somewhere else.

Hardly ever turn them all on, two on today.

 

You need a designer to calculate the heat loss. From that you can then calculate the volume flow rate required. Each of the sub circuits can then be fitted with a commissioning valve set to allow the required volume flow rate. This should resolve the issue of low flow to your upper floor. You will be able to calculate the pump head required & retain the existing or replace if the performance is inadequate. I would recommend a thorough flushing of the system in both directions then water treatment after.

None of your options are cheap but once done that’s it. I wish you good luck with this & hope that you are able to find a designer.

Good luck stay safe.