Not Getting Hot Enough!

[Nelly B]

Thanks for that desktop. Yes a circulation issue does seem to be the consensus and will investigate with my plumber. The only thing is, I thought the boiler temperature would need to be much higher say 80 or so for it to short cycle. Can I be sure the boiler is working ok?

 

[Madrab]

Is the system sealed or open vent?

If the flow is only reaching 64degC on max then it's not an overheat causing it to cycle, if that was the case then it wouldn't normally run for ages, usually an overheat occurs relatively quickly on a boiler that can't get rid of it's heat. With this one it seems the boiler is reaching set temp and that's when it short cycles.

How is the new pump set up?

 

[Nelly B]

Thank you Madrab. It’s an open vented gravity system. The Grundfos UPS4 is set to speed 2 constant pressure mode (the default).

 

[Exedon]

Tank feed / open vent id be checking pipework with a magnet around open vent/ cold feed area.

 

[ericmark]

@desktop987456 has a point, I tend to forget not everyone uses electronic TRV heads which give a code if jammed etc. My wall thermostat and two out of 10 TRV heads produce graphs so I can see how they have preformed.

If one radiator valves are stuck wide open, the returning hot water can cause the boiler to modulate, same with a by-pass valve. We tend to look for blockages, rather than the reverse. Only takes someone to have opened a lock shield valve as they were cold, to upset the whole system.

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[Nelly B]

Thank you for all your help guys.

Exedon: Bearing in mind I have a chalet bungalow, the feed and return pipes from the boiler go into the loft first, which is the same height as the upstairs as it is on top of a lounge/kitchen extension. Two pipes go off to the header tank on the far wall of the loft (feed and vent) then along and down into the airing cupboard. All of the feed pipe I could get to in the loft is magnetic (not the pipes to the tank). Also magnetic near the pump in the airing cupboard. Not magnetic on the pipe to the hot water tank from the valve or anywhere on the return to the boiler that I could get to. I assume this indicates sludge build up and maybe my problem? There is a 'Magnaclean' on the return pipe in the airing cupboard but was only fitted 7 years ago with the new bolier. House had new plumbing completely around 1994 when the bungalow was converted/extended.

Ericmark: All the radiators have TRVs but I don't generally use them so are left open. Of the 12 radiators, 7 TRVs are at the feed end of the radiator and 5 at the lockshield end. My understanding is this is OK as the TRVs are bidirectional but can make balancing more tricky?. I have balanced the radiators using the lockshield valves, i.e. closing them all but one and then opening a little as required starting with nearest the boiler. The radiators seem to warm up together but some a bit better than others.

 

[Exedon]

I'll have a bet that the pipework is restricted with crap.
Pic of one we sorted.

 

[jackthom]

As there seems to be insufficient flow to carry away the heat being produced by the boiler have you tried setting the pump to the maximum speed?

 

[ericmark]

I have balanced the radiators

So did I, worked A1 in mother's house but did not work here. I did the fine-tuning by reading the TRV display, the current should not exceed target, it can easily do this while warming up, overshooting, and harder to get spot on if the TRV is on the return, but it did work, the anti-hysteresis software seemed OTT, so would set to 22°C at 7 am and 20°C at 8 am to get around the software, took some time to get right, but it did work spot on, only when sun shining through windows would it over shoot. I was rather proud how well I had set it.

Then I moved here, and the TRV head does not work with an on/off oil boiler with micro bore, as well as they did with a gas modulating boiler, with 15 mm pipework. Main problem is the hall cools too slowly, so having the main thermostat in the hall did not work, and the Nest Gen 3 thermostat needs a 12 volt power supply from the hub, so not really an option to reposition it.

So fitted a Wiser hub in parallel, and Wiser wall thermostat in the living room, and TRV in the wife's bedroom. Living room now at the temperature I want, but a bit slow re-heating, but think that's simply down to the size of the radiators.

Of the four homes I have lived in, every one was different, home one hot air worked very well but expensive to run (1970s) Next water open plan, up-stairs got too hot, TRV heads upstairs only cured that, open-plan house, added extra radiator downstairs, but thermostat in arch between both rooms, and it worked well. (1980-2018) So mothers was a problem, cured by fitting a TRV on hall radiator with the hall thermostat. And this home sorted by fitting multi-thermostats. Seems no one system suits all.

 

[Hugh Jaleak]

Anywhere 'magnetic', i.e. your Magnet is attracted, will indicate Sludge and Crud build up, restricting the flow through the pipework, which is rather likely to be a big part, if not all, of your issue.

Depending on how much Pipework you think is affected, a Powerflush would probably be a good start to give the entire system a thorough clean, and see if there's any improvement, before condemning the pipework and replacing the most affected areas.

 

[Nelly B]

As there seems to be insufficient flow to carry away the heat being produced by the boiler have you tried setting the pump to the maximum speed?

Thank you Jackthorn but yes the pump speed does not seem to make a difference.

 

[Madrab]

Tank feed / open vent id be checking pipework with a magnet around open vent/ cold feed area.

Took the words right out of my mouth

@Nelly B - as suggested - if any of the copper pipework attracts a magnet then that's an issue and can certainly cause circulation problems and create the problems you are experiencing, hence the open vent question.

As a starting point I would run an aggressive cleaner through it and see if that dissolves any of the build up and see if that makes a difference. be careful with any strong cleaner though as it can't stay in the system overly long. Ultimately though you may be driven to replace some of the pipework, as I've rarely been able to bring a system back properly, usually by the time it is causing problems like that, it's a bit too late to shift it.

 

[Nelly B]

Thanks Madrab. That's the sort of direction my plumber was going anyway so will eventually report back how we get on.

I'm still a bit concerned regarding how the boiler is behaving in terms of short cycling - I am inclined to get it checked out and serviced first.

 

[Exedon]

I'm still a bit concerned regarding how the boiler is behaving in terms of short cycling - I am inclined to get it checked out and serviced first.

If you boiler is due for servicing crack on otherwise all the symptoms you are describing are almost certainly caused by restricted pipework.
The picture i attached was from a 11 rad system that was somehow still sort of working !
Short Cycling very sluggish eventually boiler cut out on overheat.
Unfortunately blockages around cold feed fairly common on tank feed systems.

 

[Madrab]

I'm still a bit concerned regarding how the boiler is behaving in terms of short cycling - I am inclined to get it checked out and serviced first.

That could simply be down to a flow issue, where were you getting the temps from? There isn't a flow sensor on these, rather a flow temp sensor so they don't monitor the actual flow, only the temps. If it was a circulation issue I would expect the boiler to reach max or set temp well before the rads get warm enough., which is what you are seeing

Everything discussed though does point towards blocked pipework. By all means get it serviced but without a cause, short cycling wouldn't necessarily be sorted by a service.