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Firstly, I should probably mention that I'm in the UK...

My wife and I bought a house new from a builder over 9 years ago and have had no problems whatsoever with our central heating system in that time. It is a typical modern system with a gas boiler in the kitchen feeding radiators upstairs and downstairs and a pressurised hot water system. The radiators have thermostatic valves on them (except for one in the entrance hall).

Earlier this year, I contracted a local plumber to do 4 things:

  1. Replace the original ("bimetallic") thermostat with a more modern programmable thermostat so that we could keep the heating on over night but at a lower temperature
  2. Service the boiler (for no real reason other than that it was 9+ years old and had never been looked at)
  3. Re-balance the radiators
  4. Re-pressurise the hot water system as the showers had lost their original mains water pressure

The system has never been quite right since but of course we haven't really been able to pin anything down until the recent cold weather. We are now seeing the following:

  1. For a while, the thermostat would call for heat, but the boiler wouldn't fire up. The boiler casing was very, very hot, so I suspect overheat protection had kicked in.
  2. When the boiler does fire, it doesn't stay on for more than a minute and then goes of for 2-3 minutes before firing up again. Again, suspicious that it is overheating.
  3. As a result of the above, it can take all day to get the house up to temperature (20C)

The plumber came to investigate last week and made a number of noises about the pump overrun not working, and the possibility of a pump failure, but ruled both of those out. He made some adjustments and now:

  1. The boiler appears to fire up reliably, although it does cut out periodically. He assures me this is normal and that it switches itself off while the water is circulated. I can't honestly say I was aware of it doing this before the summer.
  2. The radiators get too hot to touch, but I'd swear you used to be able to feel the heat radiating from them up to 12+ inches away which you no longer can.
  3. But still the house is very slow to heat (it appears to heat up at a bit under 1C per hour).

The house is a fairly typical British 4 bed detached (c. 1800 sqft) and is relatively modern (being newly built 9 years ago) so has pretty good thermal characteristics.

So my questions are:

  1. Does taking 8+ hours to get the house warm sound right? I'd swear it used to be warm within an hour or so of the heating coming on.
  2. What further diagnoses can I perform to help (the plumber and/or you good folks) identify the problem.
  3. Does it sound reasonable to assume (having had 9+ years of faultless service) that my problems stem from the work done in the summer? Perhaps a valve was closed while the plumber worked that he subsequently forgot to open, or something like that?

Taken together, all the symptoms sound to me like the hot water is not being circulated around the system quickly enough (boiler over temperature, house not heating up), and the plumber would appear to agree. He seems rather keen to fit a bigger pump. But I'm reluctant given that the system has worked fine for so long previously.

Sorry for the rambling post, but I'm pretty much at my wits' end with this and we have two small children that we'd really like to keep warm over the winter.

Tester101
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dty
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6 Answers6

5

So, nearly a year later I think I've got this solved! It appears that the bypass valve was left almost fully open. This explains a lot.

The "path of least resistance" is for the water to use the bypass circuit to return to the boiler instead of going around the radiators, which explains why it was taking forever for the house to heat up.

Now, the water returning to the boiler is almost as hot as the water leaving, having lost very little of its heat in the brief trip to the bypass circuit and back. This explains why the boiler shuts down very quickly. It is expecting a much larger temperature difference between the output and the return and hence gets very hot very quickly. In the mean time, the pump continues to circulate hot water around the bypass circuit.

mike
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dty
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You've bought a programmable thermostat so you can lower the temperature of the house at night, however by doing that you are making it much harder work for the boiler to bring the house back up to temperature. Before your house was at a constant temperature so you boiler would turn on for a bit, off for a bit, on a bit, off a bit over the whole day. Now it goes off for a long time and your house gets cold, then it has to run a very long time to get it back up to temperature again, leading it to overheat and shut down.

It may be your boiler simply doesn't have the grunt to heat your house for that long. Try setting your night-time temperature a bit higher and see if that improves the situation.

It could also be that your system is gunked up, leading to poor water circulation in your system. Did you have your heating engineer put a cleaner in the system? If not, have him try it.

GdD
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2

To help you compare, I'm in NY and my 2400 sqft home takes approx. 30-60 minutes to reach 20C (68F) when outdoors its 4C (40F). My house was built in 1960, but the windows are double-pane and were replaced ~8 years ago. The roof was replaced at the same time.

I'm far from an expert, but I would suggest getting a different professional to take a look. Here in NY, I have a contract with the Oil company to perform service was needed. They take care of any maintenance related to heating.

The scenario you presented, specifically that your house would heat up in a timely manner before, leads me to believe something was either changed or broken since the last maintenance. Note, I do not mean to imply it was the cause, just that it was since then.

A second professional opinion looks to be worth it.

Jose Leon
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The new digital room stats start shutting down in pulses before they reach the set temperature these pulses or gaps get longer the nearer it gets to the set temperature. This works great with a highly insulated house but feels like it never gets hot in an old house. You will have to turn up the desired temperature an extra degree to overcome it.

Dave Doogan
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Check your furnace. Every time I have this issue, it is due to the furnace. Sometimes it needs a new filter, sometimes it needs the flame sensor cleaned. I have never had an issue with the thermostat, always the furnace.

skottmorris
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Do you leave an overnight temp on at all? Also, when this happened to me, my boiler would start firing off and on even when it was 2 degrees less than what I’d asked it to get to. I started being really ridiculous and putting it up to 29 degrees just to ensure it kept firing non stop

Dan Jones
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